System and method for a delivery fiber for isolation against back reflections

ABSTRACT

An apparatus and method that provide optical isolation by permitting substantially all forward-propagating light into a delivery fiber from an optical amplifier and substantially preventing backward-traveling light from the delivery fiber entering the optical amplifier without the use of a conventional optical isolator. Eliminating the isolator improves efficiency and reduces cost. Some embodiments use a delivery fiber having a non-circular core in order to spread a single-mode signal into multiple modes such that any backward-propagating reflection is inhibited from reentering the single-mode amplifier. Some embodiments amplify an optical signal in a gain fiber having an output end, output the forward-propagating amplified signal as a high-brightness optical beam (having a first Rayleigh range) into a removable delivery fiber having a non-circular waveguide, output the amplified signal from a distal end of the delivery fiber, and, without the use of a non-linear optical isolator, inhibit backward-propagating light from re-entering the gain fiber.

This application is a divisional of and claims benefit of U.S. patentapplication Ser. No. 13/085,354 filed on Apr. 12, 2011, titled“HIGH-POWER LASER SYSTEM HAVING DELIVERY FIBER WITH NON-CIRCULAR CROSSSECTION FOR ISOLATION AGAINST BACK REFLECTIONS” by Matthias P.Savage-Leuchs (which issued as U.S. Pat. No. 8,736,953 on May 27, 2014),which claims priority under 35 U.S.C. §119(e) to U.S. Provisional PatentApplication No. 61/343,947 filed on Apr. 12, 2010, titled “HIGH-POWERLASER SYSTEM HAVING DELIVERY FIBER WITH NON-CIRCULAR CROSS SECTION FORISOLATION AGAINST BACK REFLECTIONS” by Matthias P. Savage-Leuchs, U.S.Provisional Patent Application No. 61/343,945 filed on Apr. 12, 2010,titled “Apparatus for optical fiber management and cooling” by YongdanHu et al., U.S. Provisional Patent Application No. 61/343,946 filed onApr. 12, 2010, titled “Beam diagnostics and feedback system and methodfor spectrally beam-combined lasers” by Tolga Yilmaz et al., U.S.Provisional Patent Application No. 61/343,948 filed on Apr. 12, 2010,titled “HIGH BEAM QUALITY AND HIGH AVERAGE POWER FROM LARGE-CORE-SIZEOPTICAL-FIBER AMPLIFIERS; SIGNAL AND PUMP MODE-FIELD ADAPTOR FORDOUBLE-CLAD FIBERS AND ASSOCIATED METHOD” by Matthias Savage-Leuchs etal., and U.S. Provisional Patent Application No. 61/343,949 filed onApr. 12, 2010, titled “METHOD AND APPARATUS FOR IN-LINEFIBER-CLADDING-LIGHT DISSIPATION” by Yongdan Hu, which are eachincorporated herein by reference in their entirety.

This invention is related to:

U.S. Pat. No. 6,456,756 issued Sep. 24, 2002 to Roy Mead, et al., titled“FIBER RAMAN AMPLIFIER PUMPED BY AN INCOHERENTLY BEAM COMBINED DIODELASER,”

U.S. Pat. No. 7,792,166 issued Sep. 7, 2010 to Lawrence A. Borschowa,titled “APPARATUS AND METHOD FOR DRIVING LASER DIODES”,

U.S. Pat. No. 7,620,077 issued Nov. 17, 2009 to Angus J. Henderson,titled “APPARATUS AND METHOD FOR PUMPING AND OPERATING OPTICALPARAMETRIC OSCILLATORS USING DFB FIBER LASERS”,

U.S. Pat. No. 7,701,987 issued Apr. 20, 2010 to Matthias P.Savage-Leuchs et al., titled “APPARATUS AND METHOD FOR GENERATINGCHIRP-SLICE CONTROLLED-LINEWIDTH LASER-SEED SIGNALS”,

U.S. Pat. No. 7,471,705 issued Dec. 30, 2008 to David C. Gerstenbergeret al., titled “ULTRAVIOLET LASER SYSTEM AND METHOD HAVING WAVELENGTH INTHE 200-NM RANGE”,

U.S. Pat. No. 7,391,561 issued Jun. 24, 2008 to Fabio Di Teodoro et al.,titled “FIBER—OR ROD-BASED OPTICAL SOURCE FEATURING A LARGE-CORE,RARE-EARTH-DOPED PHOTONIC-CRYSTAL DEVICE FOR GENERATION OF HIGH-POWERPULSED RADIATION AND METHOD”,

U.S. Pat. No. 7,430,352 issued Sep. 30, 2008 to Fabio Di Teodoro et al.,titled “MULTI-SEGMENT PHOTONIC-CRYSTAL-ROD WAVEGUIDES FOR AMPLIFICATIONOF HIGH-POWER PULSED OPTICAL RADIATION AND ASSOCIATED METHOD”,

U.S. Pat. No. 7,379,648 issued May 27, 2008 to Christopher D. Brooks etal., titled “OPTICAL HOLLOW-CORE DELIVERY FIBER AND HOLLOW-ENDCAPTERMINATION AND ASSOCIATED METHOD”,

U.S. Pat. No. 7,386,211 issued Jun. 10, 2008 to Fabio Di Teodoro et al.,titled “METHOD AND APPARATUS FOR SPECTRAL-BEAM COMBINING OFMEGAWATT-PEAK-POWER BEAMS FROM PHOTONIC-CRYSTAL RODS”,

U.S. Pat. No. 7,400,804 issued Jul. 15, 2008 to Fabio Di Teodoro et al.,titled “MONOLITHIC OR RIBBON-LIKE MULTI-CORE PHOTONIC-CRYSTAL FIBERS ANDASSOCIATED METHOD”,

U.S. Pat. No. 7,429,734 issued Sep. 30, 2008 to Steven C. Tidwell,titled “SYSTEM AND METHOD FOR AIRCRAFT INFRARED COUNTERMEASURES TOMISSILES”,

U.S. Pat. No. 7,199,924 issued on Apr. 3, 2007 to Andrew J. W. Brown etal., titled “APPARATUS AND METHOD FOR SPECTRAL-BEAM COMBINING OFHIGH-POWER FIBER LASERS”,

U.S. Pat. No. 7,768,700 issued Aug. 3, 2010 to Matthias P.Savage-Leuchs, titled “METHOD AND APPARATUS FOR OPTICAL GAIN FIBERHAVING SEGMENTS OF DIFFERING CORE SIZES”,

U.S. Pat. No. 7,872,794 issued Jan. 18, 2011 to John D. Minelly et al.,titled “HIGH-ENERGY EYE-SAFE PULSED FIBER AMPLIFIERS AND SOURCESOPERATING IN ERBIUM'S L-BAND”,

U.S. patent application Ser. No. 12/624,327 titled “SPECTRALLY BEAMCOMBINED LASER SYSTEM AND METHOD AT EYE-SAFER WAVELENGTHS” filed on Nov.23, 2009 by Roy D. Mead (which issued as U.S. Pat. No. 8,441,718 May 14,2013),

U.S. Provisional Patent Application 61/263,736 filed Nov. 23, 2009 byMatthias P. Savage-Leuchs et al., titled “Q-switched oscillatorseed-source for MOPA laser illuminator method and apparatus”, and

U.S. patent application Ser. No. 12/854,868 titled “IN-LINEFORWARD/BACKWARD FIBER-OPTIC SIGNAL ANALYZER” filed on Aug. 11, 2010 byTolga Yilmaz et al. (which issued as U.S. Pat. No. 8,755,649 on Jun. 17,2014),

which are all incorporated herein in their entirety by reference.

FIELD OF THE INVENTION

The invention relates generally to optical waveguides and moreparticularly to delivery waveguides for reducing the amount ofback-reflected light that is coupled back into an amplifying or lasingoptical fiber and associated damage to high-power master-oscillatorpower-amplifier (MOPA) laser systems, wherein, in some embodiments, oneor more delivery waveguides are formed in a delivery fiber, and thedelivery fiber has a non-circular waveguide and a mode-fieldadaptor/beam collimator that work together to prevent back reflectionsfrom a distal end of the delivery fiber from propagating back into thepower-amplifier stage, and wherein, in some embodiments, the deliveryfiber is connectorized and/or sterilized and is considered disposableand replaceable.

BACKGROUND OF THE INVENTION

High-power laser systems (for example, laser systems employing amaster-oscillator power-amplifier (MPOA) configuration) are subject todamage if a back-reflected signal from a distal end of a delivery fiberre-enters the power-amplifier stage. Typically, circular fibers are usedas delivery fibers for pulsed and continuous-wave (CW) laser signals.However, it has been shown (M. Fermann, “Single-mode excitation ofmultimode fibers with ultrashort pulses”, OPTICS LETTERS/Vol. 23, No.1/Jan. 1, 1998, which is incorporated herein by reference) that thefundamental mode in a fiber can propagate in multimode fibers over longdistances. Therefore, when a reflection occurs after the laser lightexits the delivery fiber, laser light can propagate backwards in thedelivery fiber and maintain or nearly maintain its beam quality.Consequently, reflected signals can be coupled into the amplifier andlead to damage of the amplifier or laser. To prevent this, conventionalsystems typically employ an optical isolator that allows onlyone-directional signal propagation in a direction away from the poweramplifier. Such isolators are expensive and complex.

U.S. Pat. No. 7,576,909 issued to Harter, et al. on Aug. 18, 2009 titled“Multimode amplifier for amplifying single mode light,” and isincorporated herein by reference. Harter et al. describe techniques forthe control of the spatial as well as spectral beam quality ofmulti-mode fiber amplification of high-peak-power pulses, as well asusing such a configuration to replace diode-pumped, Neodynium basedsources. Harter et al. assert that perfect spatial beam-quality can beensured by exciting the fundamental mode in the multi-mode fibers withappropriate mode-matching optics and techniques. The loss of spatialbeam-quality in the multi-mode fibers along the fiber length can beminimized by using multi-mode fibers with large cladding diameters. Neardiffraction-limited coherent multi-mode amplifiers can be convenientlycladding pumped, allowing for the generation of high average power.Moreover, the polarization state in the multi-mode fiber amplifiers canbe preserved by implementing multi-mode fibers with stress producingregions or elliptical fiber cores.

U.S. Pat. No. 7,590,323 to Broeng et al. issued Sep. 15, 2009 titled“Optical fibre with high numerical aperture, method of its production,and use thereof” and is incorporated herein by reference. Broeng et al.describe an optical fiber, having at least one core surrounded by afirst outer cladding region, the first outer cladding region beingsurrounded by a second outer cladding region, the first outer claddingregion in the cross-section comprising a number of first outer claddingfeatures having a lower refractive index than any material surroundingthe first outer cladding features, wherein for a plurality of said firstouter cladding features, the minimum distance between two nearestneighboring first outer cladding features is smaller than 1.0 μm orsmaller than an optical wavelength of light guided through the fiberwhen in use; a method of its production, and use thereof. They alsodescribe fibers built from performs having non-circular tubes or rodsthat form non-circular cores for the collection of light from laserdiodes having non-symmetric non-circular beams.

A paper in the 30 Oct. 2006 Vol. 14, No. 22 of OPTICS EXPRESS pages10345-10350 by J. R. Hayes et al. titled “Square core jacketed air-cladfiber” is incorporated herein by reference. Hayes et al. describefabrication of a highly multi-mode square core jacketed air-clad fiberwith a top-hat near-field intensity profile, and using this fiber todeliver Q-switched pulses to ablate square marks on indium tin oxidefilms.

There is a need for improved laser systems, particularly optical-fiberlasers and/or optical-fiber amplifiers having delivery fibers, whereinsystems have improved optical isolation to prevent optical feedback dueto reflections in the delivery fiber or at its ends from traveling backinto, and damaging, the optical-fiber lasers and/or optical-fiberamplifiers. There is also a need to eliminate a conventional isolator toreduce the cost, size and complexity of the system.

SUMMARY OF THE INVENTION

In some embodiments, the present invention provides a method, anapparatus, and disposable parts thereof for a laser-delivery fiber thathas a non-circular core cross-sectional area. In some embodiments, thesignal-light output from a relatively small-core gain fiber is directedinto a relatively large-core gain fiber that has a non-circular core. Insome embodiments, signal light is coupled from a higher brightness fiberto a lower brightness fiber. In some embodiments, the gain fiber can beslightly multimoded. As used herein, the proximal end of the deliveryfiber is the light-input end next to the gain fiber of the laser oroptical amplifier that provides the signal light, while the distal endis the opposite light-output end at which the signal light is used ordirected from. The forward-propagating signal light that enters theproximal delivery fiber is well mixed by the geometry of the core of thedelivery fiber, and any reflections from the distal end of the deliveryfiber (due, for example, to its design, its use (e.g., from, bonesand/or metal pieces in case of a wounded soldier, blood or tissue thatmay be next to or deposit on the end), or from damage to the distal endof the delivery fiber) that become unwanted backward-propagating lightwill be further mixed such that multiple modes of the reflected signallight will return from the entry end of the delivery fiber, and only avery small portion (generally at a power level that is 20-30 dB lessthan the output beam power) will re-enter the gain fiber. In someembodiments, the end of the delivery fiber is angled relative to theoutput beam of the gain fiber, but has a sufficiently high numericalaperture (e.g., NA=0.2 to 0.3) that substantially all the output beamfrom the gain fiber enters the core (the signal waveguide) of thedelivery fiber; on the other hand, in some embodiments, the gain fiberhas an NA of only 0.1 or so and back-reflected light from the deliveryis at too steep an angle to re-enter the gain fiber as undesiredbackward-traveling signal light that can damage the gain fiber orvarious components (such as pump laser diodes) connected to the gainfiber. In some embodiments, the delivery fiber has an endcap attached toits entry end, wherein the endcap has a non-circular or a non-centeredentry aperture that is sized and/or located such that it acceptssubstantially all the output light from the gain fiber traveling in theforward direction, but wherein the aperture of the entry endcap has asize, shape and/or offset from the core axis of the delivery-fiber thatblocks a substantial amount of any backward signal reflections from theexit end of the delivery fiber. In some embodiments, the center axis ofthe core of the gain fiber is offset from the center axis of the core ofthe delivery fiber, also with the purpose that the larger NA of thedelivery fiber will receive substantially all of the output beam fromthe gain fiber, but the smaller NA of the gain fiber will receive only avery small portion of and backward-traveling light reflected from thefar end of the delivery fiber. In some embodiments, a combination of themode mixing of the non-circular-core delivery fiber, the angled entryend of the delivery fiber, the size/shape/offset of the entry apertureor endcap, and/or the offset of the center axes of the cores of the twofibers work together to synergistically reduce the backward-travelingreflected signal light. In some embodiments, the delivery fiber isconnectorized to enable it to be disposable and easily replaced. This isan important consideration for medical and other applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of a prior-art optical subsystem 101 thatincludes an optical gain fiber having a core interfaced to a multi-modedelivery fiber.

FIG. 1B is a block diagram of a prior-art optical subsystem 102 thatincludes an optical gain fiber having a core interfaced through anoptical isolator 122 to a multi-mode delivery fiber.

FIG. 1C is a cross-section block diagram of a prior-art single-modeoptical fiber 103 that includes circular single-mode core 141 surroundedby cladding layer 140.

FIG. 1D is a cross-section block diagram of a prior-art multi-modeoptical fiber 104 that includes a large-diameter circular multi-modecore 142 surrounded by cladding layer 140.

FIG. 2 is a block diagram of an improved optical subsystem 201 thatincludes an optical gain fiber 210 having a core interfaced through afeedback-isolation-and-adaptor unit 220 to a multi-mode delivery fiber231 having a non-circular core, according to some embodiments of thepresent invention.

FIG. 3 is a block diagram of an improved subsystem 301 that includes anamplifier system 310 for amplifying a seed pulse 91 and outputting theamplified signal 98 into a feedback-isolation-and-adaptor unit 320 thatis connected to a multi-mode delivery fiber 331 having a non-circularcore, according to some embodiments of the present invention.

FIG. 4A is a block diagram of subsystem 401 that includes a multi-modedelivery fiber 431 having a non-circular core, according to someembodiments of the present invention.

FIG. 4B is a block diagram of subsystem 402 that includes an offsetmulti-mode delivery fiber 432, according to some embodiments of thepresent invention.

FIG. 4C is a block diagram of subsystem 403 that includes a tiltedmulti-mode delivery fiber 433, according to some embodiments of thepresent invention.

FIG. 4D is a block diagram of subsystem 404 that includes a tilted andoffset multi-mode delivery fiber 434, according to some embodiments ofthe present invention.

FIG. 4E is a block diagram of subsystem 405 that includes a multi-modedelivery fiber 431 having a reverse endcap 439, according to someembodiments of the present invention.

FIG. 4F is a block diagram of subsystem 406 that includes an offsetmulti-mode delivery fiber 432 having a reverse endcap 439, according tosome embodiments of the present invention.

FIG. 4G is a block diagram of subsystem 407 that includes a tiltedmulti-mode delivery fiber 433 having a reverse endcap 439, according tosome embodiments of the present invention.

FIG. 4H is a block diagram of subsystem 408 that includes a tilted andoffset multi-mode delivery fiber 434 having a reverse endcap 439,according to some embodiments of the present invention.

FIG. 5A is a block diagram of optical subsystem 501 that includes anoptical gain fiber 510 having a core optically coupled through a pair ofcollimating lens (521 and 523) to a multi-mode delivery fiber 531 havinga non-circular core, according to some embodiments of the presentinvention.

FIG. 5B is a block diagram of optical subsystem 502 that includes anoptical gain fiber 510 having a core optically coupled through a pair ofcollimating lens (521 and 523), one or more apertures 524, and one ormore highly reflective mirrors 525 to a multi-mode delivery fiber 531having a non-circular core, according to some embodiments of the presentinvention.

FIG. 6A is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 601 that includes a non-circular multi-mode core 641surrounded by cladding layer 640, according to some embodiments of thepresent invention.

FIG. 6B is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 602 that includes a non-circular multi-mode core 642surrounded by cladding layer 640, according to some embodiments of thepresent invention.

FIG. 6C is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 603 that includes a non-circular multi-mode core 643surrounded by cladding layer 640, according to some embodiments of thepresent invention.

FIG. 6D is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 604 that includes a non-circular multi-mode core 644surrounded by cladding layer 640, according to some embodiments of thepresent invention.

FIG. 6E is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 605 that includes a non-circular multi-mode core 645surrounded by cladding layer 640, according to some embodiments of thepresent invention.

FIG. 6F is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 606 that includes a non-circular multi-mode core 646surrounded by cladding layer 640, according to some embodiments of thepresent invention.

FIG. 6G is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 607 that includes a non-circular multi-mode core 647surrounded by cladding layer 640, according to some embodiments of thepresent invention.

FIG. 6H is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 608 that includes a non-circular multi-mode core 648surrounded by cladding layer 640, according to some embodiments of thepresent invention.

FIG. 6I is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 609 that includes a non-circular multi-mode core 645surrounded by an inner cladding layer 640, which is in turn surroundedby an outer protective cladding 649, according to some embodiments ofthe present invention.

FIG. 6J is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 610 that includes a non-circular multi-mode core 641surrounded by cladding layer 640 and a mask 638 having an offsetlight-entry aperture 639, according to some embodiments of the presentinvention.

FIG. 6K is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 611 that includes a non-circular multi-mode core 651surrounded by air-cladding or photonic-crystal layer 661 and outercladding layer 660, according to some embodiments of the presentinvention.

FIG. 6L is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 612 that includes a non-circular pentagonal-shapedmulti-mode core 652 surrounded by air-cladding or photonic-crystal layer661 and outer cladding layer 660, according to some embodiments of thepresent invention.

FIG. 6M is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 613 that includes a non-circular hexagonal-shapedmulti-mode core 653 surrounded by air-cladding or photonic-crystal layer661 and outer cladding layer 660, according to some embodiments of thepresent invention.

FIG. 6N is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 614 that includes a non-circular octagonal-shapedmulti-mode core 654 surrounded by air-cladding or photonic-crystal layer661 and outer cladding layer 660, according to some embodiments of thepresent invention.

FIG. 6o is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 615 that includes a non-circular substantiallysquare-shaped multi-mode core 655 surrounded by air-cladding orphotonic-crystal layer 662 and outer cladding layer 660, according tosome embodiments of the present invention.

FIG. 6P is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 616 that includes a non-circular substantiallyrectangular-shaped multi-mode core 656 surrounded by air-cladding orphotonic-crystal layer 662 and outer cladding layer 660, according tosome embodiments of the present invention.

FIG. 6Q is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 617 that includes a non-circular star-shaped multi-modecore 657 surrounded by air-cladding or photonic-crystal layer 661 andouter cladding layer 660, according to some embodiments of the presentinvention.

FIG. 6R is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 618 that includes a non-circular star-shaped multi-modecore 658 surrounded by air-cladding or photonic-crystal layer 661 andouter cladding layer 660, according to some embodiments of the presentinvention.

FIG. 6S is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 619 that includes a non-circular substantiallysquare-shaped multi-mode core 664 surrounded by air-cladding orphotonic-crystal layer 661, and outer cladding layer 660, which is inturn surrounded by an outer protective cladding 669, according to someembodiments of the present invention.

FIG. 6T is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 620 that includes a non-circular multi-mode core 671surrounded by air-cladding layer 661 and cladding layer 660 thatincludes a non-circular pentagonal-shaped multi-mode core 671 surroundedby air-cladding or photonic-crystal layer 661 and outer cladding layer660, according to some embodiments of the present invention. and a mask638 having an offset light-entry aperture 639, according to someembodiments of the present invention.

FIG. 6U is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 621 that includes a non-circular substantiallysquare-shaped multi-mode core 665 surrounded by air-cladding orphotonic-crystal layer 661 and outer cladding layer 660, according tosome embodiments of the present invention.

FIG. 6V is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 622 that includes a non-circular multi-mode core 641surrounded by a cladding layer 640, according to some embodiments of thepresent invention, and a mask 638 having an offset light-entry aperture639, according to some embodiments of the present invention.

FIG. 7 is a block diagram of apparatus 701 that includes non-circularcore optical delivery fiber 731 that is sterilized and enclosed insterilized package 770, according to some embodiments of the presentinvention.

FIG. 8 is a block diagram of an instrument system 801 having ahigh-power mode-field-adaptor fiber-laser control system using one ormore of the mode-field-adaptor fiber-laser systems as described herein.

FIG. 9A is a block diagram of apparatus 901 that includes non-circularcore optical delivery fiber 931 and connector 911B, according to someembodiments of the present invention.

FIG. 9B is a block diagram of apparatus 902 that includes non-circularcore optical delivery fiber 931 inserted through connector 911B,according to some embodiments of the present invention.

FIG. 9C is a block diagram of apparatus 903 that includes non-circularcore optical delivery fiber 931 and connector 911B, according to someembodiments of the present invention.

FIG. 9D is a block diagram of apparatus 904 that includes non-circularcore optical delivery fiber 931, connector 911B and adaptor 911A,according to some embodiments of the present invention.

FIG. 10A is a block diagram of apparatus 1001 that includes non-circularcore optical delivery fiber 1031 inserted through angled connector1011B, according to some embodiments of the present invention.

FIG. 10B is a block diagram of apparatus 1002 that includes non-circularcore optical delivery fiber 1031 and angled connector 1011B, accordingto some embodiments of the present invention.

FIG. 10C is a block diagram of apparatus 1003 that includes non-circularcore optical delivery fiber 1031, connector 1011C and straight adaptor1011A, according to some embodiments of the present invention.

FIG. 10D is a block diagram of apparatus 1004 that includes non-circularcore optical delivery fiber 1031, connector 1011D and straight adaptor1011A, according to some embodiments of the present invention.

FIG. 11A is a block diagram of an improved optical subsystem 1101 thatincludes an optical gain fiber 210 having a core interfaced through afeedback-isolation-and-adaptor unit 220 to a multi-mode delivery fiber231 having a non-circular core, wherein thefeedback-isolation-and-adaptor unit 1120 includes mirror 1175A,according to some embodiments of the present invention.

FIG. 11B is a block diagram of an improved optical subsystem 1102 thatincludes an optical gain fiber 210 having a core interfaced through afeedback-isolation-and-adaptor unit 220 to a multi-mode delivery fiber231 having a non-circular core, wherein thefeedback-isolation-and-adaptor unit 1120′ includes mirror 1175B,according to some embodiments of the present invention.

DETAILED DESCRIPTION

Although the following detailed description contains many specifics forthe purpose of illustration, a person of ordinary skill in the art willappreciate that many variations and alterations to the following detailsare within the scope of the invention. Accordingly, the followingpreferred embodiments of the invention are set forth without any loss ofgenerality to, and without imposing limitations upon the claimedinvention. Further, in the following detailed description of thepreferred embodiments, reference is made to the accompanying drawingsthat form a part hereof, and in which are shown by way of illustrationspecific embodiments in which the invention may be practiced. It isunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the present invention.

The leading digit(s) of reference numbers appearing in the Figuresgenerally corresponds to the Figure number in which that component isfirst introduced, such that the same reference number is used throughoutto refer to an identical component that appears in multiple figures.Signals and connections may be referred to by the same reference numberor label, and the actual meaning will be clear from its use in thecontext of the description.

FIG. 1A is a block diagram of a prior-art optical subsystem 101 thatincludes an optical gain fiber having a core interfaced to a multi-modedelivery fiber. According to this configuration the optical signal 91from a seed source is amplified in gain fiber 110 and becomes amplifiedforward-traveling signal 98 that is interfaced into a conventionalmulti-mode delivery fiber 130 by lens 121. According to Ferman's 1998paper (M. Fermann, “Single-mode excitation of multimode fibers withultrashort pulses”, OPTICS LETTERS/Vol. 23, No. 1/Jan. 1, 1998) the highquality output of gain fiber 110 will be conveyed down the multi-modefiber 130 substantially intact and without loss. This is less thandesirable in certain applications such as medical laser energy deliverybecause of the concentration of energy in the center of the Gaussianoutput beam. In addition, this configuration has the undesirable qualityof also conveying any reflected signal 97 (such as the reflection fromhuman tissue, other objects in the environment, imperfections in or onthe output end of the delivery fiber, and the like) substantially intactand without loss and will reenter the gain fiber in the backwardtraveling direction where signal 97 will be further amplified and causeundesirable heating and other damage to the gain fiber and its pumpsources. One conventional way to alleviate some of these problems is touse an optical isolator, such as shown in FIG. 1B, however this addssubstantial cost to the system and also does not address the problem ofhaving the energy of the output beam 98 concentrated at the center ofthe Gaussian beam when it lands on the tissue 99.

FIG. 1B is a block diagram of a prior-art optical subsystem 102 thatincludes an optical gain fiber having a core interfaced through anoptical isolator unit 120 to a multi-mode delivery fiber. Thisconfiguration addresses the problem of backward traveling beams(described in FIG. 1A above) by introducing a 20 dB to 30 dB loss in thebackward traveling beam (such as may re-enter the delivery fiber 130from a reflection from human tissue or other object in the environmentas described above. This configuration does not address the issue ofenergy concentrated at the center of the Gaussian beam and also has theundesirable result of the isolator 122 reducing power in the forwardtraveling beam due to the inherent properties of the isolator 122.Subsystem 102 also includes and input ferrule 112 that releasableconnects gain fiber 110 to isolator 120, and output ferrule 111 thatreleasable connects delivery fiber 130 to isolator unit 120. Isolatorunit 120 further includes collimating lens 121 that collimates theforward traveling beam from gain fiber 110 and directs the collimatedbeam to isolator 122 and collimating lens 123 that focuses thecollimated beam from isolator 122 into the core of delivery fiber 130.

FIG. 1C is a block diagram cross-sectional view of a prior-artsingle-mode optical fiber 103 that includes circular single-mode core141 surrounded by cladding layer 140 and FIG. 1D is a block diagramcross-sectional view of a prior-art multi-mode optical fiber 104 thatincludes circular multi-mode core 142 surrounded by cladding layer 140.Conventional optical systems use a delivery fiber having either asingle-mode circular core (e.g., optical fiber 103) when a thin cut orincision is desired or a multi-mode circular core (e.g., optical fiber)when a more uniform power output is desired.

As used herein, “feedback isolation” is optical isolation that permitssignal light propagation in a forward direction, but inhibits signallight propagation in the opposite (backward) direction. As used herein,an “adaptor unit” includes an interface from one optical subsystem (suchas an optical power amplifier) and another optical subsystem (such as adelivery fiber).

FIG. 2 is a block diagram of an improved optical subsystem 201 thatincludes an optical gain fiber 210 having a core interfaced through afeedback-isolation-and-adaptor unit 220 to a multi-mode delivery fiber231 having a non-circular core, according to some embodiments of thepresent invention. In some embodiments of the present invention, opticalsubsystem 201 addresses the both the problem of backward traveling beams(described in FIG. 1A above) and the issue of energy concentrated at thecenter of the Gaussian output beam (also described above in FIG. 1A).Optical subsystem 201 addresses the issue of optical energy beingconcentrated at the center of a Gaussian beam (i.e., one wherein thespatial cross-section exhibits a Gaussian profile) by using a deliveryfiber 231 that has a non-circular core which has the effect of causingthe single-mode forward-traveling amplified beam 98 to be mode mixed inthe non-circular core delivery fiber 231, even over short distances. Incontrast to the Gaussian beam output by prior-art optical subsystems 101and 102 using optical fiber 103 and 104, optical subsystem 201 of thepresent invention will output a beam with a significantly degraded beamquality, wherein the optical energy of the output beam will besubstantially uniform over the area of the beam spot. Having a beam spotwith uniform output energy is very desirable in many applications,including medical laser treatment procedures. The issue of backwardtraveling beams caused by reflections of the output beam from humantissue, other objects in the operational environment, imperfections inor on the output end of the delivery fiber, or the like, is alsoaddressed in the present invention with the use of the non-circular coredelivery fiber 231. In the situation of the backward traveling reflectedbeam, the non-circular core delivery fiber 231 is used to protect aoptical subsystem 201 because, when the light output from thenon-circular delivery fiber 231 is reflected back into the deliveryfiber 231 propagates in a backward direction towards the amplifying gainfiber 210, only a small amount of light is coupled back into the gainfiber 210. The worst case of coupling of the backward traveling beaminto the gain fiber 210 corresponds to the brightness difference betweenthe delivery fiber 231 and the gain fiber 210. As described in thepresent invention, laser systems with non-circular delivery fibers canachieve isolation of about 20 dB to 30 dB without requiring the use ofan isolator unit and such isolation is capable and sufficiently high toisolate and protect against feedback reflections.

In some embodiments, the present invention provides isolation againstoptical feedback by using non-circular delivery fibers, isolation levelsof 20 dB-40 dB, a reduction in insertion loss even without the use of anisolator, a reduction in the laser power required because an isolator isnot used, and further, non circular deliver fibers have the addedbenefit of producing a top-hat intensity profile and provides an optimuminteraction of the optical radiation with treated tissue.

Optical subsystem 201 of the present invention also includes a seedsource 209 optically coupled to fiber amplifier 210 that provides anoptical signal into the core of the gain fiber 210, input ferrule 212that releasable connects gain fiber 210 to isolator and adaptor unit220, and output ferrule 211 that releasable connects delivery fiber 231to isolator and adaptor unit 220. Isolator and adaptor unit 220 furtherincludes lens 221 that focuses the forward traveling beam 98 from gainfiber 210 and into the non-circular core of delivery fiber 231.Additionally, in some embodiments, optical subsystem 201 furtherincludes a mode stripper 214 coupled to the gain fiber 210 to removeunwanted optical light from the cladding of the gain fiber 210 and amatching single-clad fiber 215 connected between the output end of thegain fiber 210 and the input ferrule 212 which acts like a pinhole andeliminates light which would otherwise propagate in the pump cladding ofthe gain fiber 210 and might lead to damage of the pump diodes. In someembodiments, the cladding of the delivery fiber 231 is single-clad andis anti-guiding and therefore strips any light coupled into itscladding.

FIG. 3 is a block diagram of an improved optical subsystem 301 thatincludes an amplifier system 310 for amplifying a seed pulse 91 andoutputting the amplified signal 98 into a feedback-isolation-and-adaptorunit 320 that is connected to a multi-mode delivery fiber 331 having anon-circular core, according to some embodiments of the presentinvention. In some embodiments, amplifier system 310 is a two-stageamplifying system that includes first optical pump 318 opticallyconnected to amplifier 317 through optical fiber 316 and a secondoptical pump 318 optically connected to amplifier 319 through opticalfiber 316. In some embodiments, seed source 309 is configured to outputoptical seed pulse 91 and provide optical seed source 91 to amplifiersystem 310. Amplifier system 310 is configured to receive optical seedpulse 91 and amplify the seed pulse in the first amplifier 317 and thesecond amplifier 318 and output amplified optical pulse to the isolationand adaptor unit 320. In some embodiments, amplified optical pulse 98propagates through isolation and adaptor unit 320 and is output intonon-circular multi-mode delivery fiber 331, wherein the amplifiedoptical pulse 98 is mode mixed and output through endcap 329 as outputpulse 92 from the exit end of the non-circular multi-mode delivery fiber331, resulting in output pulse 92 having a generally uniform powerdensity.

FIG. 4A is a block diagram of subsystem 401 that includes a multi-modedelivery fiber 431 having a non-circular core, a connector 411B,according to some embodiments of the present invention. In someembodiments, subsystem 401 is similar to optical subsystem 201 of FIG.2, described above, in that subsystem 401 also addresses both theproblem of backward traveling beams (described in FIG. 1A above) and theissue of energy concentrated at the center of the Gaussian output beam(also described above in FIG. 1A), through the use of non-circulardelivery fiber 431. In some embodiments, subsystem 401 also includes aconnector 411B that is attached to the entrance end of the deliveryfiber 431 and connector 411B is configured to connect and disconnect toadaptor 411A. In some embodiments, adaptor 411A and connector 411Bcombine together as ferrule 411 and provide a means for connecting anddisconnecting the delivery fiber to the isolator and adaptor unit 420.In some embodiments, subsystem 401 includes amplifying fiber 410configured to output amplified light 98 into isolator and adaptor unit420. Isolator and adaptor unit 420 further includes lens 421, which isconfigured to focus amplified light signal 98 that is output by a fiberamplifier 410 (as described above in FIG. 2) into the entry end ofnon-circular delivery fiber 431.

FIGS. 4B-4H, show additional embodiments according to the presentinvention reduces the amount of backward traveling reflected light thatenters the amplifier fiber, thereby improving the achievable isolationto even more sufficiently isolate and protect the optical subsystemagainst feedback reflections. In some embodiments, the subsystems inFIGS. 4B-4H also address the issue of energy concentrated at the centerof the Gaussian output beam (also described above in FIG. 1A) by using anon-circular core delivery fiber. FIGS. 4B-4H each include fiberamplifier 410 configured to output amplified light into isolator andadaptor unit 420 as described above for FIG. 4A and further includeslens 421 configured to focus amplified light 98 into the delivery fiberand adaptor 411A configured to connect and disconnect from connector411B and together with connector 411B forms a ferrule. In someembodiments, each subsystem described in FIGS. 4B-4H include an aperture(not shown) that allows substantially all of amplified light 98 to passthrough, but prevents a portion of the backward traveling reflectedlight from passing through and thus further reduces the amount ofreflected light that enters the fiber amplifier 410.

FIG. 4B is a block diagram of subsystem 402 that includes an offsetmulti-mode delivery fiber 432, according to some embodiments of thepresent invention. In some embodiments, subsystem 402 further reducesthe amount of backward traveling reflected light from entering theamplifying stage of the optical subsystem and damaging the opticalsubsystem by offsetting the placement of the entry end of delivery fiber432 in connector 411B a linear distance away from an optical axis 96created by amplified light 98 being focused by lens 421. That is, insome embodiments, the delivery fiber connector is configured such thatthe axis of the core of the delivery fiber is substantially parallel tothe axis of the core of the amplifying fiber and/or to a central axis 96of the focused beam from lens 421 and/or to a central axis of the lens421, but wherein the axis of the core of the delivery fiber is radiallyoffset from the axis of the core of the amplifying fiber and/or from thecentral axis of the focused beam from lens 421 and/or from a centralaxis of the lens 421. In some embodiments, this radial offset isaccomplished by mounting the fiber into its connector 411B such that thecentral axis of the fiber is radially offset from the central axis ofthe connector, and the adaptor 411A is concentric with the central axisof lens 421 and the end of the core of amplifying fiber 410, while inother embodiments, the fiber is mounted into its connector 411B suchthat the central axis of the fiber is concentric with the central axisof the connector, and the adaptor 411A is radially offset to the centralaxis of lens 421 and the end of the core of amplifying fiber 410, whilein still other embodiments, the fiber is mounted into its connector 411Bsuch that the central axis of the fiber is concentric with the centralaxis of the connector and the adaptor 411A is concentric to the end ofthe core of amplifying fiber 410, but the central axis of lens 421 isradially offset from these axes. In some embodiments, delivery fiber 432has a numerical aperture (NA) sufficiently large (in some suchembodiments, a diffraction-limited beam at the output of a20-micron-core-diameter gain fiber has an approximate NA of about 0.04(when the signal beam has a 1-micron wavelength)-0.08 (when the signalbeam has a 2-micron wavelength), therefore a delivery fiber having anumerical aperture that is at least two times the NA of the gain fibermakes sense, and thus some embodiments use a delivery fiber having an NAof at least 0.2) to accept substantially all of the focused amplifiedlight 98 into the core of delivery fiber 432 and amplifying fiber 410has a sufficiently small NA such that substantially none of thebackward-traveling reflected light enters fiber amplifier 410. In someembodiments, delivery fiber 432 has a non-circular core to cause mixingof the single-mode amplified light 98 such that the light output bydelivery fiber 432 has a more uniform energy profile. In someembodiments, the lateral (in the radial direction) distance by which theoptical axis of the entry end of deliver fiber 432 is offset fromoptical axis 96 by an amount that is one to two times the diameter ofthe mode profile of the signal beam at the output of the gain fiber, orone to two times the diameter of the core of the gain fiber. In otherembodiments, the linear distance by which the center longitudinal axisof the entry end of deliver fiber 432 is offset from the centerlongitudinal optical axis 96 is more than 0.25 times, but less than one(1) times the mode field diameter of the signal beam at the output ofthe gain fiber. In still other embodiments, the linear distance by whichthe center longitudinal axis of the entry end of deliver fiber 432 isoffset from the center longitudinal optical axis 96 is at least 1.2times, or at least 1.4 times, or at least 1.6 times, or at least 1.8times, or at least 2.0 times the mode field diameter of the signal beamat the output of the gain fiber.

For example, in some embodiments having a gain fiber with an NA of about0.04, the delivery fiber has an NA of at least 0.07, while in otherembodiments having a gain fiber with an NA of about 0.04, the deliveryfiber has an NA of at least 0.08, an NA of at least 0.09, an NA of atleast 0.10, an NA of at least 0.11, an NA of at least 0.12, an NA of atleast 0.14, an NA of at least 0.16, an NA of at least 0.18, an NA of atleast 0.20, an NA of at least 0.22, or even an NA of at least 0.24.

For another example, in some embodiments having a gain fiber with an NAof 0.08, the delivery fiber has an NA of at least 0.15, while in otherembodiments having a gain fiber with an NA of about 0.08, the deliveryfiber has an NA of at least 0.16, an NA of at least 0.18, an NA of atleast 0.20, an NA of at least 0.22, an NA of at least 0.24, an NA of atleast 0.26, an NA of at least 0.28, or even an NA of at least 0.3.

FIG. 4C is a block diagram of subsystem 403 that includes a tilted-endmulti-mode delivery fiber 433, according to some embodiments of thepresent invention. In some embodiments, subsystem 403 further reducesthe amount of backward traveling reflected light from entering theamplifying stage of the optical subsystem and damaging the opticalsubsystem by tilting the entry end of delivery fiber 433 relative to thecentral axis of connector 411B such that an angle is formed between thetilted end of delivery fiber 433 and an optical axis 96 created byamplified light 98 being focused by lens 421, however the entry end ofdelivery fiber 433 (i.e., the end surface of delivery fiber 433 whereinamplified light signal 98 enters delivery fiber 433) continues to belined up with optical axis 96. In other embodiments, the delivery fiberconnector is configured such that the axis of the core of the deliveryfiber is substantially parallel to the central axis of connector 411B,but the central axis of adaptor 411A is tilted relative to optical axis96, the core of the amplifying fiber and/or to a central axis of thefocused beam from lens 421 and/or to a central axis of the lens 421. Insome other embodiments, this tilt is accomplished by mounting the fiberinto its connector 411B such that the central axis of the fiber isparallel to and centered on the central axis of the connector, and theadaptor 411A is concentric with the end of the core of amplifying fiber410, but the central axis of lens 421 is tilted relative to the axis ofdelivery fiber 433. In some embodiments, delivery fiber 433 has anumerical aperture (NA) sufficiently large (e.g., an NA of at least0.15) to accept substantially all of the focused amplified light 98 intothe tilted core of delivery fiber 432 and amplifying fiber 410 has asufficiently small NA such that substantially none of thebackward-traveling reflected light exiting delivery fiber 433 at anangle with respect to optical axis 96 enters fiber amplifier 410. Insome embodiments, delivery fiber 433 has a non-circular core to causemixing of the single-mode amplified light 98 such that the light outputby delivery fiber 433 has a more uniform energy profile. In someembodiments, the angle between the axis of the delivery fiber at theentry end of deliver fiber 433 and the optical axis 96 of the output endof the gain fiber is about 0.05 radians (wherein the delivery fiber hasan NA of at least about 0.05 (which is the sine of 0.05 radians)) toabout 0.5 radians (wherein the delivery fiber has an NA of at leastabout 0.48 (which is the sine of 0.5 radians)). This range is equal toabout 3 degrees, wherein the delivery fiber has an NA of at least about0.052; to about 30 degrees, wherein the delivery fiber has an NA of atleast 0.5. In other embodiments, this angle is about 0.1 radians, about0.15 radians, about 0.2 radians, about 0.25 radians, about 0.3 radians,about 0.35 radians, about 0.4 radians, or about 0.45 radians.

FIG. 4D is a block diagram of subsystem 404 that includes atilted-and-offset-end multi-mode delivery fiber 434, according to someembodiments of the present invention. In some embodiments, subsystem 404further reduces the amount of backward traveling reflected light fromentering the amplifying stage of the optical subsystem and damaging theoptical subsystem by both offsetting the placement of the entry end ofdelivery fiber 434 with respect to an optical axis 96 created byamplified light 98 being focused by lens 421 and by tilting the entryend of delivery fiber 434 in connector 411B such that an angle is formedbetween the tilted end of delivery fiber 434 and an optical axis 96. Inother embodiments, the delivery fiber connector is configured such thatthe axis of the core of the delivery fiber is substantially parallel tothe central axis of connector 411B, but the central axis of adaptor 411Ais tilted and offset relative to optical axis 96, the core of theamplifying fiber and/or to a central axis of the focused beam from lens421 and/or to a central axis of the lens 421. In some other embodiments,this tilt and offset is accomplished by mounting the fiber into itsconnector 411B such that the central axis of the fiber is parallel toand centered on the central axis of the connector, and the adaptor 411Ais concentric with the end of the core of amplifying fiber 410, but thecentral axis of lens 421 is radially offset and tilted relative to theaxis of delivery fiber 433. In some embodiments, delivery fiber 434 hasa numerical aperture (NA) sufficiently large (e.g., in some embodiments,an NA of at least about 0.16) to accept substantially all of the focusedamplified light 98 into the offset and tilted core of delivery fiber 434and amplifying fiber 410 has a sufficiently small NA such thatsubstantially none of the backward-traveling reflected light exitingdelivery fiber 434 offset and at an angle with respect to optical axis96 enters fiber amplifier 410. In some embodiments, delivery fiber 434has a non-circular core to cause mixing of the single-mode amplifiedlight 98 such that the light output by delivery fiber 434 has a moreuniform energy profile. In some embodiments, the linear distance bywhich the center longitudinal axis of the entry end of deliver fiber 434is offset from the center longitudinal optical axis 96 is at least onetimes the mode field diameter of the signal beam as it exits the gainfiber. In other embodiments, the linear distance by which the centerlongitudinal axis of the entry end of deliver fiber 434 is offset fromthe center longitudinal optical axis 96 is at least 1.2 times, or atleast 1.4 times, or at least 1.6 times, or at least 1.8 times, or atleast 2.0 times the mode field diameter. In some embodiments, the anglebetween the entry end of deliver fiber 434 and the optical axis 96 isabout 0.05 radians to about 0.5 radians. In other embodiments, the anglebetween the entry end of deliver fiber 434 and the optical axis 96 is atleast about 0.1 radians, at least about 0.15 radians, at least about 0.2radians, at least about 0.25 radians, at least about 0.3 radians, atleast about 0.35 radians, at least about 0.4 radians, or at least about0.45 radians, but in each of these cases less than about 1 radian.

FIG. 4E is a block diagram of subsystem 405 that includes a multi-modedelivery fiber 431 having a reverse endcap 439 connected betweenconnector 411B and delivery fiber 431, according to some embodiments ofthe present invention. In some embodiments, subsystem 405 issubstantially similar to subsystem 401 described above, howeversubsystem 405 also includes reverse endcap 439 that further degrades thebackward-traveling reflected light and thus further reduces the amountof backward-traveling reflected light that enters fiber amplifier 410.In some embodiments, reverse endcap 439 includes a short section offiber having a core (either substantially circular or non-circular) thatis larger than the core of non-circular delivery fiber 431. In someembodiments, the reverse endcap 439 having its larger core fiber sectiondegrades the reflected light propagating backwards in delivery fiber431. In some embodiments, the maximum length of the reverse endcap 439is chosen so that when the amplified light 98 from fiber amplifier 410propagates (in the forward direction) through reverse endcap 439, thebrightness of the amplified light 98 does not degrade in the endcap morethan the brightness of amplified light that propagates through thesmaller core-size delivery fiber 431 would degrade. However, reverseendcap 439 further degrades the brightness of reflected lightpropagating backwards and therefore reverse endcap 439 will reduce thecoupling of the reflected light into the fiber amplifier 410.

FIG. 4F is a block diagram of subsystem 406 that includes an offsetmulti-mode delivery fiber 432 having a reverse endcap 439, according tosome embodiments of the present invention. In some embodiments,subsystem 406 is substantially similar to subsystem 402 described above,however subsystem 406 also includes reverse endcap 439 that furtherdegrades the backward-traveling reflected light and thus further reducesthe amount of backward-traveling reflected light that enters fiberamplifier 410.

FIG. 4G is a block diagram of subsystem 407 that includes a tiltedmulti-mode delivery fiber 433 having a reverse endcap 439, according tosome embodiments of the present invention. In some embodiments,subsystem 407 is substantially similar to subsystem 403 described above,however subsystem 407 also includes reverse endcap 439 that furtherdegrades the backward-traveling reflected light and thus reverse endcap439 further reduces the amount of backward-traveling reflected lightthat enters fiber amplifier 410.

FIG. 4H is a block diagram of subsystem 408 that includes a tilted andoffset multi-mode delivery fiber 434 having a reverse endcap 439,according to some embodiments of the present invention. In someembodiments, subsystem 408 is substantially similar to subsystem 404described above, however subsystem 408 also includes reverse endcap 439that further degrades the backward-traveling reflected light and thusreverse endcap 439 further reduces the amount of backward-travelingreflected light that enters fiber amplifier 410.

FIG. 5A is a block diagram of optical subsystem 501 that includes anoptical gain fiber 510 having a core optically coupled through a pair ofcollimating lens (521 and 523) to a multi-mode delivery fiber 531 havinga non-circular core, according to some embodiments of the presentinvention. In some embodiments, optical subsystem 501 includes a opticalfiber amplifier 510 configured to amplify optical light signal 91 andoutput amplified light signal 98 from the output end of gain fiber 510.In some embodiments, collimating lens 521 is optically coupled to theoutput end of gain fiber 510 and receives and collimates amplified lightsignal 98. In some embodiments, lens 523 is optically coupled to theinput end of delivery fiber 531 and receives the collimated amplifiedlight signal 98 from lens 521 and focuses the amplified light signal 98into the input end of the non-circular core delivery fiber 531.Amplified light signal 98 propagates through multi-mode delivery fiber531 where amplified light signal 98 is mixed and is output through theoutput end of non-circular core delivery fiber 531 where the amplifiedlight signal 98 interacts with sample 99. In some embodiments, the modemixing of the amplified light signal 98 that occurs during propagationthrough the non-circular core multi-mode delivery fiber 531 causes theoutput amplified light signal to have a more uniform energy density. Insome embodiments, backward-traveling light 97 is generated byreflections of the light signal 98 with the sample 99 as well as otherinterfaces and imperfections within optical system 501 and propagatesthrough the delivery fiber in a direction opposite to the amplifiedlight signal 98 where it will exit from the input end of delivery fiber531. In some embodiments, the beam quality of backwards propagatinglight signal 97 is highly degraded due to the non-circular core ofdelivery fiber 531 and therefore backward-traveling light 97 will have aRayleigh range that is shorter than the Rayleigh range of theforward-traveling amplifier light signal 98. In some embodiments, thedistance between lens 521 and lens 523 is selected such thatbackward-traveling light 97 will significantly diverge and overfill lens521, whereby the fraction of the coupled power of backward-travelinglight 97 into gain fiber 510 is significantly reduced. In someembodiments, the distance d between lens 521 and lens 523 isd≧NA_(DF)*f₅₂₃/(M²*λ) wherein NA_(DF) the NA of the non-circulardelivery fiber 531, f₅₂₃ the focal length of lens 523, M² is the beamquality of the light coming back from the delivery fiber 531, λ, is thelaser wavelength of the signal beam. In some further embodiments, anaperture 524 is inserted between lens 521 and lens 523 to providefurther reduction of backward-traveling light 97, for example, when thefiber used on the output of the amplifier 510 is a double clad fiber. Instill further embodiments, an enclosure 528 includes an adaptor 411A(such as shown in FIG. 4A) configured to receive a connector 411B, whichis used on the end of the delivery fiber 531 (such as shown in FIG. 4A)and the offset and/or tilting mechanism described above in FIGS. 4B-4Dis used for tilting and/or offsetting lens 521 and/or 523 and/or fortilting and/or offsetting connector 411B and/or adaptor 411A to furtherreduce the amount of backward-traveling reflected light 97 that canenter fiber amplifier 510.

FIG. 5B is a block diagram of optical subsystem 502 that includes anoptical gain fiber 510 having a core optically coupled through a pair ofcollimating lens (521 and 523), one or more apertures 524, and one ormore highly reflective mirrors 525 to a multi-mode delivery fiber 531having a non-circular core, according to some embodiments of the presentinvention. In some embodiments, optical subsystem 502 utilizes theincreased Rayleigh range of the backward-traveling light 97, asdiscussed above for FIG. 5A, in a compact arrangement. In someembodiments, optical subsystem 502 includes isolator and adaptor unit520 which includes collimating lens 521 configured to collimateamplified light signal 98, one or more highly reflective mirrors 525configured to reflect forward-traveling amplified light signal 98, andcollimating lens 523 configured to focus forward-traveling light signal98 into the non-circular core of delivery fiber 531. In someembodiments, the one or more highly-reflecting mirrors 525 increase thepath length that amplified light signal 98 and backward-traveling lightsignal 97 travel between lens 521 and lens 523 in a compact manner.Using the configuration of subsystem 502, the optical path lengthbetween lens 521 and lens 523 is, in some embodiments, increased inorder to further decrease the amount of backward-traveling light 97 thatis coupled into the gain fiber 510 in a compact manner withoutsacrificing performance. In some embodiments, optical subsystem furtherincludes input ferrule 512, which includes connector 512B and adaptor512A and allows gain fiber 510 to be connected and disconnected toisolator and adaptor unit 520. In some embodiments, optical subsystemfurther includes output ferrule 511, which includes connector 511B andadaptor 511A and allows delivery fiber 531 to be connected anddisconnected to isolator and adaptor unit 520. In some embodiments,isolator and adaptor unit 520 further includes one or more apertures 524for further reducing the amount of backward-traveling light 97 that iscoupled into gain fiber 510. In some embodiments, the optical pathlength between lens 521 and lens 523 is greater than the Rayleigh lengthof the backward-traveling light signal 97, but shorter than theforward-traveling amplified light signal 98. In still furtherembodiments, the offset and/or tilting mechanism described above inFIGS. 4B-4D is used for tilting and/or offsetting lens 521 and/or 523and/or for tilting and/or offsetting connector 411B and/or adaptor 411Ato further reduce the amount of backward-traveling reflected light 97that can enter fiber amplifier 510.

FIG. 6A is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 601 that includes a non-circular multi-mode core 641surrounded by cladding layer 640, according to some embodiments of thepresent invention. In some embodiments, the non-circular core 641 issubstantially oval in shape.

FIG. 6B is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 602 that includes a non-circular multi-mode core 642surrounded by cladding layer 640, according to some embodiments of thepresent invention. In some embodiments, the non-circular core 642 issubstantially a polygon in shape (e.g., in some embodiments, a regularpolygon such as an equilateral triangle, a square, a pentagon, ahexagon, a heptagon, an octagon or other regular polygon, while in otherembodiments, the core is a non-regular polygon such as a non-squarerectangle or other polygonal shape). In yet other embodiments, the corehas any non-circular shape such as an oval or wavy curved circumference.In still other embodiments, the core is round but has stress rods, areasof higher or lower index of refraction, or similar elements in it. Suchelements lead to enhanced mode coupling. In yet still other embodiments,an airclad or photonic crystal structure is used around the core (e.g.,forming a core that is quasi round), for example, such as theembodiments described in FIG. 6K through 6V.

FIG. 6C is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 603 that includes a non-circular multi-mode core 643surrounded by cladding layer 640, according to some embodiments of thepresent invention. In some embodiments, the non-circular core 641 issubstantially hexagonal in shape.

FIG. 6D is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 604 that includes a non-circular multi-mode core 644surrounded by cladding layer 640, according to some embodiments of thepresent invention. In some embodiments, the non-circular core 641 issubstantially octagonal in shape.

FIG. 6E is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 605 that includes a non-circular multi-mode core 645surrounded by cladding layer 640, according to some embodiments of thepresent invention. In some embodiments, the non-circular core 641 issubstantially square in shape.

FIG. 6F is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 606 that includes a non-circular multi-mode core 646surrounded by cladding layer 640, according to some embodiments of thepresent invention. In some embodiments, the non-circular core 641 issubstantially rectangular in shape.

FIG. 6G is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 607 that includes a non-circular multi-mode core 647surrounded by cladding layer 640, according to some embodiments of thepresent invention. In some embodiments, the non-circular core 647 isshaped as substantially a star-shaped polygon having both concave andconvex vertices.

FIG. 6H is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 608 that includes a non-circular multi-mode core 648surrounded by cladding layer 640, according to some embodiments of thepresent invention. In some embodiments, the non-circular core 648 isshaped as substantially a star-shaped polygon having both concave andconvex vertices, but with fewer vertices than the embodiment shown inFIG. 6G.

FIG. 6I is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 609 that includes a non-circular multi-mode core 649surrounded by cladding layer 640 and cladding layer 640 is surrounded byadditional cladding, “cabling,” and/or armor layers (e.g., in someembodiments, a triple-clad fiber) layer 649, according to someembodiments of the present invention. In some embodiments, thenon-circular core 645 is shown as being substantially square in shape,however, other embodiments use a non-circular core of any suitablynon-circular shape, including those described in the previous figures.

FIG. 6J is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 610 that includes a non-circular multi-mode core 641surrounded by cladding layer 640 and a mask 638 having an offsetlight-entry aperture 639, according to some embodiments of the presentinvention. In some embodiments, the aperture is located such that amajority of the signal light from the gain fiber can enter the deliveryfiber through the aperture 639, but a majority of the reflected signallight from the delivery fiber is blocked by the mask so it cannotre-enter the gain fiber, according to some embodiments of the presentinvention. In some embodiments, the aperture 639 is located and offsetfrom the optical center of the optical delivery fiber 610 such that onlya portion 637 of the aperture 639 overlaps with the non-circular core641, such that a majority of the signal light from the gain fiber canenter the delivery fiber through the aperture 639, but a majority of thereflected signal light from the delivery fiber is blocked by the mask soit cannot re-enter the gain fiber.

FIG. 6K is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 611 that includes a non-circular multi-mode core 651surrounded by air-cladding or photonic-crystal layer 661 and outercladding layer 660, according to some embodiments of the presentinvention. In some embodiments, fiber 611 of FIG. 6K is substantiallysimilar to fiber 601 of FIG. 6A described above, except that fiber 611includes an air-cladding layer 661 to provide additional mode mixing ofthe optical signal in the optical delivery fiber 611.

FIG. 6L is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 612 that includes a non-circular pentagonal-shapedmulti-mode core 652 surrounded by air-cladding layer 661 and claddinglayer 660, according to some embodiments of the present invention. Insome embodiments, fiber 612 of FIG. 6L is substantially similar to fiber602 of FIG. 6B described above, except that fiber 612 includes anair-cladding layer 661 to provide additional mode mixing of the opticalsignal in the optical delivery fiber 612.

FIG. 6M is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 613 that includes a non-circular hexagonal-shapedmulti-mode core 653 surrounded by air-cladding layer 661 and claddinglayer 660, according to some embodiments of the present invention. Insome embodiments, fiber 613 of FIG. 6M is substantially similar to fiber603 of FIG. 6C described above, except that fiber 613 includes anair-cladding layer 661 to provide additional mode mixing of the opticalsignal in the optical delivery fiber 613.

FIG. 6N is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 614 that includes a non-circular octagonal-shapedmulti-mode core 654 surrounded by air-cladding layer 661 and claddinglayer 660, according to some embodiments of the present invention. Insome embodiments, fiber 614 of FIG. 6N is substantially similar to fiber604 of FIG. 6D described above, except that fiber 614 includes anair-cladding layer 661 to provide additional mode mixing of the opticalsignal in the optical delivery fiber 614.

FIG. 6o is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 615 that includes a non-circular substantiallysquare-shaped multi-mode core 655 surrounded by air-cladding layer 662and cladding layer 660, according to some embodiments of the presentinvention. In some embodiments, fiber 615 of FIG. 6o is substantiallysimilar to fiber 605 of FIG. 6E described above, except that fiber 615includes an air-cladding layer 662 to provide additional mode mixing ofthe optical signal in the optical delivery fiber 615.

FIG. 6P is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 616 that includes a non-circular substantiallyrectangular-shaped multi-mode core 656 surrounded by air-cladding layer662 and cladding layer 660, according to some embodiments of the presentinvention. In some embodiments, fiber 616 of FIG. 6P is substantiallysimilar to fiber 606 of FIG. 6F described above, except that fiber 616includes an air-cladding layer 662 to provide additional mode mixing ofthe optical signal in the optical delivery fiber 616.

FIG. 6Q is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 617 that includes a non-circular star-shaped multi-modecore 657 surrounded by air-cladding layer 661 and cladding layer 660,according to some embodiments of the present invention. In someembodiments, Figure fiber 617 of 6Q is substantially similar to fiber607 of FIG. 6G described above, except that fiber 617 includes anair-cladding layer 661 to provide additional mode mixing of the opticalsignal in the optical delivery fiber 617.

FIG. 6R is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 618 that includes a non-circular star-shaped multi-modecore 658 surrounded by air-cladding layer 661 and cladding layer 660,according to some embodiments of the present invention. In someembodiments, Figure fiber 618 of 6R is substantially similar to fiber608 of FIG. 6H described above, except that fiber 618 includes anair-cladding layer 661 to provide additional mode mixing of the opticalsignal in the optical delivery fiber 618.

FIG. 6S is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 619 that includes a non-circular substantiallysquare-shaped multi-mode core 664 surrounded by air-cladding layer 661,and cladding layer 660, which is in turn surrounded by an outerprotective cladding 669, according to some embodiments of the presentinvention. In some embodiments, fiber 619 of FIG. 6S is substantiallysimilar to fiber 609 of FIG. 6I described above, except that fiber 619includes an air-cladding layer 661 to provide additional mode mixing ofthe optical signal in the optical delivery fiber 619.

FIG. 6T is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 620 that includes a non-circular multi-mode core 671surrounded by air-cladding layer 661 and cladding layer 660 thatincludes a non-circular pentagonal-shaped multi-mode core 671 surroundedby air-cladding layer 661 and cladding layer 660, according to someembodiments of the present invention, and a mask 638 having an offsetlight-entry aperture 639, according to some embodiments of the presentinvention. In some embodiments, fiber 620 of FIG. 6T is substantiallysimilar to fiber 610 of FIG. 6J described above, except that fiber 620includes an air-cladding layer 661 to provide additional mode mixing ofthe optical signal in the optical delivery fiber 620. In someembodiments, the aperture 639 is located and offset from the opticalcenter of the optical delivery fiber 620 such that only a portion 637 ofthe aperture 639 overlaps with the non-circular core 671, such that amajority of the signal light from the gain fiber can enter the deliveryfiber through the aperture 639, but a majority of the reflected signallight from the delivery fiber is blocked by the mask so it cannotre-enter the gain fiber. In some embodiments, the aperture 639 isoriented at an “apogee” end of core 637 as is shown in FIG. 6J ratherthan as shown in this FIG. 6T.

FIG. 6U is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 621 that includes a non-circular substantiallysquare-shaped multi-mode core 665 surrounded by air-cladding layer 661and cladding layer 660, according to some embodiments of the presentinvention. In some embodiments, fiber 621 of FIG. 6U is substantiallysimilar to fiber 605 of FIG. 6E described above, except that thenon-circular substantially square-shaped core 665 of fiber 621 issmaller than the substantially-square core 645 of FIG. 6E, and inaddition fiber 621 further includes an air-cladding layer 661 to provideadditional mode mixing of the optical signal in the optical deliveryfiber 611.

FIG. 6V is a block diagram cross-sectional view of a multi-mode opticaldelivery fiber 622 that includes a non-circular multi-mode core 641surrounded by a cladding layer 640, according to some embodiments of thepresent invention. and a mask 638 having an offset light-entry aperture639, according to some embodiments of the present invention. In someembodiments, delivery fiber 622 is substantially identical to deliveryfiber 610 of FIG. 6J, however mask 638 is oriented such that aperture639 is aligned to receive core light from the flat side of oval core641, rather than from the “apogee” end of the oval core 641, as was thecase in FIG. 6J.

FIG. 7 is a block diagram of apparatus 701 that includes a deliveryfiber assembly 741, having a non-circular core optical delivery fiber731, that is sterilized and enclosed in package 770, according to someembodiments of the present invention. In some embodiments, apparatus 701is used in a sterilized environment (e.g., a surgical operating room orthe like) and the non-circular core optical delivery fiber 731 isremoved from the sterilized package 770 and is connected to a lasersystem (e.g., those systems shown in FIG. 2, 3, 4A-4H, 5A, 5B, 8, 11A,or 11B) using adaptor 711B for the purpose of delivering an outputoptical pulse or signal through distal endcap 729 to a target (e.g.,animal or human tissue, or the like). In some embodiments, after use,delivery fiber 731 can be disposed of (or, in some embodiments,sterilized and re-packaged). In various embodiments, each one of theembodiments described herein uses a delivery fiber assembly having adistal endcap as described for FIG. 7 here.

FIG. 8 is a block diagram of an instrument system 801 having ahigh-power fiber-laser control system using one or more of the opticalsubsystems as described herein. In some embodiments, instrument system801 (e.g., a medical instrument such as a laser scalpel, opticalstimulator for evoking nerve-action potentials in nerves of a human,skin or corneal ablator, or other medical instrument, or a materialprocessor instrument (such as for heat treatment of a surface, orwelding or cutting) or the like) using one or more of the fiberamplifiers 810 as described herein. In some embodiments, system 801includes the instrument and/or facility enclosure 880 and its othercontents (e.g., engines and control systems), one or more battery and/orelectrical power supplies 881, a laser controller 882 that provides thecontrol of wavelength, pulse timing and duration for embodiments usingpulse signals (other embodiments use CW signal beams), output-powercontrol, direction control of the output beam and the like, optionallyan imaging-calculation microprocessor and/or circuitry 884 that obtainsan image signal from imager 886 and calculates such data as targetlocation and size that is then delivered to laser controller 882, one ormore signal processor 883 that, in some embodiments, receiveswavelength-determination signals and/or directional-drift signals fromthe beam pointer module 885 (with its associated wavelength-,beam-off-axis and beam-off-angle detection sensors and circuitry, asdescribed in U.S. Pat. No. 7,199,924 issued Apr. 3, 2007 to Andrew J. W.Brown et al., titled “Apparatus and method for spectral-beam combiningof high-power fiber lasers,” which is incorporated herein by reference),and that delivers wavelength-correction control data to laser controller882. In some embodiments, laser controller 882 generates the control andpower signals that are sent to fiber-laser module 200, which thendelivers the high-power optical beam to beam pointer module 885, thatpoints and outputs a single output laser beam 92 that is directed towardtarget 99 (e.g., a tissue of a person to be treated or analyzed, or amaterial to be conditioned, welded or cut), according to the controlinformation that was generated based on image information obtained fromimager 886, or as directed by manual control of the device 880 or itsbeam pointer 885. In some embodiments, system 801 is part of, and usedas an element of, a nerve-stimulation and surgical cutting/ablationmedical instrument whose output is automatically controlled to preventundesired damage to collateral tissue (such as described in commonlyassigned U.S. Patent Application Publication 2008/0077200 titled“APPARATUS AND METHOD FOR STIMULATION OF NERVES AND AUTOMATED CONTROL OFSURGICAL INSTRUMENTS” by Bendett et al., which is incorporated herein byreference). In some embodiments, system 801 is an entire system thatuses the delivery fiber 831 according to the present invention, andbenefits by not allowing reflections from the patient (i.e., the targetof the laser radiation from the distal end of the delivery fiber) fromtraveling back into the delivery fiber and thence into the gain fiber.System 801 also benefits from having an easily replaceable and steriledelivery fiber (such as described above in FIG. 7) that does not need anexpensive isolator to provide this isolation function.

In some embodiments, the present invention provides a method formanufacturing an optical delivery fiber having a non-circular core and aconnector, such that the delivery fiber is configured to be connectedand disconnected to a system (e.g., a medical-treatment laser system, orthe like). FIG. 9A is a block diagram of apparatus 901 that includesnon-circular core optical delivery fiber 931 and connector 911B,according to some embodiments of the present invention. In someembodiments, connector 911B further includes one or more short radiallyoriented pegs 960 (used for an insert-twist-lock connection and removalcapability) and has a cylindrical hole 962 that extends from connectorsurface 963 through connector 911B to connector surface 964 configuredto accept optical delivery fiber 931. In some embodiments, the diameterof cylindrical hole 962 is slightly larger than the diameter of deliveryfiber 931 (e.g., in some embodiments, about 10 microns to 30 micronslarger diameter). In some embodiments, the insertion end of hole 962 isflared or chamfered to facilitate insertion of the delivery fiber 931.

FIG. 9B is a block diagram of apparatus 902 that shows non-circular coreoptical delivery fiber 931 inserted through connector 911B and extendingout through connector surface 964 a distance, d, 969. In someembodiments, optical delivery fiber 931 is secured in cylinder 962. Insome embodiments, the delivery fiber 931 is secured in hole 962 by laserwelding, or using adhesive, solder, or the like. In some embodiments,the exposed end 969 of the delivery fiber 931 is cleaved or polished asdescribed below.

FIG. 9C is a block diagram of apparatus 903 that shows non-circular coreoptical delivery fiber 931 extending through cylinder 962 of connector911B such that the end of delivery fiber 931 is coplanar with connectorsurface 964. In some embodiments, delivery fiber 931 and connectorsurface 964 are made coplanar by removing the section of delivery fiber931 that extended beyond connector surface 964 in FIG. 9B. In variousembodiments, exposed fiber end section 969 is removed by cleaving,polishing, cutting, or the like, such that the end of the fiber 931 isflush with the inside end of connector 911B.

FIG. 9D is a block diagram of apparatus 904 that shows non-circular coreoptical delivery fiber 931 attached to connector 911B. Connector 911B isconfigured to releasably attach to adaptor 911A (in some embodiments,pegs 960 insert and twist into slots 966 in adaptor 911A), and together,connector 911B and adaptor 911A combine to form ferrule 911 which allowsdelivery fiber 931 to be connected and disconnected to a system capableof outputting laser light. In some embodiments (e.g., laser systemshaving very high power), the delivery fiber is typically notbutt-coupled, as the power levels are too high, and thus in such systemshaving high average power, a lens is added adjacent the delivery fiberand used to relay an image of the signal beam with a magnification ontothe entry end of the delivery fiber, and this image can be greater thanone times the spotsize of the signal beam as it exits the gain fiber. Insome embodiments, adaptor 911A further includes optical fiber 910attached to adaptor 911A, diverging lens 975 configured to expandforward-propagating light signal 98 to fill first focusing lens 976having a first focal length, focusing lens 976 is configured to receiveforward-propagating light signal 98 output from plano-concave lens 975(or other optical element that causes the signal beam to diverge) suchthat the focused light from focusing lens 976 passes through aperture977, and a second focusing lens 978 having a second focal length (e.g.,a shorter focal length, in some embodiments) is configured to pass thefocused signal light 98 received from the first focussing lens 976 andto then focus the signal light 98 onto the core of the delivery fiber931. In some embodiments, the first focal length of the first focusinglens 976 is substantially longer than the second focal length of thesecond focusing lens 978. In some embodiments, backward-propagatingreflected-light 97 will be substantially blocked or otherwise preventedfrom traveling from the delivery fiber 931 into optical fiber 910because the backward-propagating reflected-light 97 will pass throughthe second focusing lens 978 and, because the second focusing lens 978has a short focal length, will be substantially blocked by aperture 976.In FIG. 9D, dotted line 95 represents the location of connector side 964when the connector 911B and the adaptor 911A have been connectedtogether. In some embodiments, optical fiber 910 further includes anintegrated beam expanding end cap (e.g., as described in U.S. Pat. No.7,835,068 titled “PHOTONIC-CRYSTAL-ROD OPTICAL AMPLIFIER WITHSEALED-HOLE ENDCAP AND ASSOCIATED METHOD” that issued Nov. 16, 2010 toChristopher D. Brooks, et al.) to prevent damage to the end of opticalfiber 910 due to high-power laser pulses output by the optical fiber910.

FIG. 10A is a block diagram of apparatus 1001 that includes non-circularcore optical delivery fiber 1031 inserted through angled connector1011B, according to some embodiments of the present invention. FIG. 10Ais substantially the same as FIG. 9B, described above, except thatconnector surface 1064 is not perpendicular to the longitudinal axis offiber 1031. In some embodiments, the outer connector surface 1063 issubstantially perpendicular to the axis of delivery fiber 1031, and theangle between a plane that is perpendicular to the longitudinal axis offiber 1031 and the plane of inner connector surface 1064 is a suitableangle between about 5 to about 30 degrees.

FIG. 10B is a block diagram of apparatus 1002 that includes non-circularcore optical delivery fiber 1031 and angled connector 1011B, accordingto some embodiments of the present invention. FIG. 10B is substantiallythe same as FIG. 9C, described above, except that, as described in FIG.10A above, connector surface 1064 is not perpendicular to thelongitudinal axis of fiber 1031 and therefore the end of delivery fiber1031 is coplanar with connector surface 1064 and is not perpendicular tothe longitudinal axis of fiber 1031. In some embodiments, angledconnector 1011B is configured to connect to an adaptor 1011A such asshown in FIG. 10C.

As shown in FIG. 10C and FIG. 10D, a plurality of types and geometriesof adaptors are used in various embodiments for connecting to angledconnectors 1011B, 1011C or 1011D. FIG. 10C is a block diagram ofapparatus 1003 that shows non-circular core optical delivery fiber 1031,angled connector 1011C and straight adaptor 1011A, according to someembodiments of the present invention. FIG. 10D is a block diagram ofapparatus 1004 that includes non-circular core optical delivery fiber1031, connector 1011D and straight adaptor 1011A, according to someembodiments of the present invention. In FIG. 10C, connector 1011C (andin FIG. 10D, connector 1011D), the respective connectors are configuredto releasably attach to adaptor 1011A, and together, connector 1011C andadaptor 1011A combine to form ferrule 1011 which allows delivery fiber1031 to be connected and disconnected to a system capable of outputtinglaser light. (As used herein, the “ferrule” refers to a combination of a“connector” at the end of the fiber, and an “adaptor” on a fixture orenclosure, wherein the adaptor releasably receives and holds theconnector.) In some embodiments, adaptor 1011A further includes opticalfiber 1010 attached to adaptor 1011A, diverging optical element such asa concave lens 1075 configured to expand forward-propagating lightsignal 98 to fill a first focusing lens 1076 having a first focallength, wherein focusing lens 1076 is configured to receiveforward-propagating light signal 98 output from diverging lens 1075 suchthat the focused light passes through aperture 1077, and a secondfocusing lens 1078 having a second focal length that is configured topass the focused light received from the first focussing lens 1076 andto then focus the signal light 98 onto the core of the delivery fiber1031. In some embodiments, the first focal length of the first focusinglens 1076 is substantially longer than the second focal length of thesecond focusing lens 1078. In some embodiments, backward-propagatingreflected-light 97 will be substantially prevented from traveling fromthe delivery fiber 1031 to optical fiber 1010 because thebackward-propagating reflected-light 97 will pass through the secondfocusing lens 1078 and, because the second focusing lens 1078 has ashort focal length, will be expanded and the periphery will besubstantially blocked by aperture 1076. In FIG. 10 C (and FIG. 10D),dotted line 95 represents the location of connector side 1064 when theconnector 1011C (or connector 1011D) and the adaptor 1011A have beenconnected together. In some embodiments, optical fiber 1010 furtherincludes an integrated beam expanding end cap (e.g., as described inU.S. Pat. No. 7,835,068 titled “PHOTONIC-CRYSTAL-ROD OPTICAL AMPLIFIERWITH SEALED-HOLE ENDCAP AND ASSOCIATED METHOD” that issued Nov. 16, 2010to Christopher D. Brooks et al.) to prevent damage to the end of opticalfiber 1010 due to high-power laser pulses output by the optical fiber1010.

FIG. 11A is a block diagram of an improved optical subsystem 1101 thatincludes an optical gain fiber 210 having a core interfaced through afeedback-isolation-and-adaptor unit 1120 to a multi-mode delivery fiber231 having a non-circular core, wherein thefeedback-isolation-and-adaptor unit 1120 includes mirror 1175Aconfigured to transmit a majority of forward-propagating amplifiedsignal 98 and to reflect a minority of amplified signal 98 for analysispurposes, according to some embodiments of the present invention. Insome embodiments, FIG. 11A is substantially similar tofeedback-isolation-and-adaptor unit 220 of FIG. 2, described above,except that additional lenses 223, 1173, and 1174, and mirror 1175A havebeen added to the feedback-isolation-and-adaptor unit 1120 such that asmall portion of forward-propagating amplified signal 98 is reflected toone or more sensors 1176 and a portion of the backward-propagatingreflected amplified light 96 is provided to one or more sensors 1177.Delivery fiber 231 is, in some embodiments, is configured according toany of the methods and apparatus described above for FIGS. 2, 3, 4A, 4B,4C, 4D, 4E, 4F, 4G, 4H, 5A, 5B, 6A, 6B, 6C, 6D, 6E, 6F, 6G, 6H, 6I, 6J,6K, 6L, 6M, 6N, 6 o, 6P, 6Q, 6R, 6S, 6T, 6U, 6V, 7, 8, 9A, 9B, 9C, 9D,10A, 10B, 10C, or 10D.

In some embodiments, beamsplitting mirror 1175A transmits about 99.5% ofthe incident amplified signal 98 and reflects about 0.5% of the incidentamplified signal. In some other embodiments, mirror 1175A transmitsabout 99.0% of the incident amplified signal 98 and reflects about 1.0%of the incident amplified signal. In some other embodiments, mirror1175A transmits about 98.5% of the incident amplified signal 98 andreflects about 1.5% of the incident amplified signal. In some otherembodiments, mirror 1175A transmits about 98.0% of the incidentamplified signal 98 and reflects about 2.0% of the incident amplifiedsignal. In some other embodiments, mirror 1175A transmits about 95.0% ofthe incident amplified signal 98 and reflects about 5.0% of the incidentamplified signal. In some other embodiments, mirror 1175A transmitsabout 90.0% of the incident amplified signal 98 and reflects about 10.0%of the incident amplified signal.

In some embodiments, feedback-isolation-and-adaptor unit 1120 includesfocusing lens 1173 configured to focus the reflected portion 98′ of theamplified light 98 that is reflected from mirror 1175A into ferrule 1171in order to provide the reflected portion 98′ to the one or more sensors1176. In some embodiments, feedback-isolation-and-adaptor unit 1120further includes focusing lens 1174 configured to focus the reflectedportion 97′ of light reflected by mirror 1175A from abackward-propagating signal 97 into ferrule 1172 in order to provide thereflected light to one or more sensors 1177. In some embodiments, mirror1175A provides the ability to simultaneously tap forward-propagating andbackward-propagating optical signals in optic laser system 1101 forsensing, analysis and/or control (e.g., in some embodiments, the tappedsignals are used to control a feedback loop that controls operation oflaser system 1101).

In some embodiments, optical laser system 1101 further includes a seedsource 209 (e.g., in some embodiments, seed source 209 includes a lasersuch as a diode laser or an optical-fiber laser that is optically pumpedusing light from a diode-laser system) that generates an optical seedsignal (in other embodiments, a controlled-bandwidth ASE source is usedfor generating the seed signal, such as described in U.S. Pat. No.7,539,231 issued May 26, 2009 to Eric C. Honea et al. titled “Apparatusand method for generating controlled-linewidth laser-seed-signals forhigh-powered fiber-laser amplifier systems,” which is incorporatedherein by reference). In some embodiments, an optical fiber carryingseed signal is connected between seed source 209 and the input port of apump dump 1191, which passes light of the wavelength of the seed signalbut which “dumps” (blocks, diverts or otherwise absorbs) light of thewavelength of the pump light from seed laser 209 or backward-propagatingpump light from optical power amplifier 1196 (also called anoptical-amplifier subsystem 1196). In some embodiments, system 1101omits a two-port optical isolator 1122 that would be used for isolatinghigh-power optical signals (e.g., in various embodiments, suchhigh-power pulses are pulses having a peak power of at least 1000 watts,or even at least 10,000 watts, at least 100,000 watts, or even at least1,000,000 watts); and instead uses the isolation techniques andmechanisms as described in FIGS. 2, 3, 4A, 4B, 4C, 4D, 4E, 4F, 4G, 4H,5A, 5B, 6A, 6B, 6C, 6D, 6E, 6F, 6G, 6H, 6I, 6J, 6K, 6L, 6M, 6N, 6 o, 6P,6Q, 6R, 6S, 6T, 6U, 6V, 7, 8, 9A, 9B, 9C, 9D, 10A, 10B, 10C, or 10D. Inother embodiments, isolator 1122 is included and supplements thoseadditional isolation techniques and mechanisms. In some embodiments,system 1101 also includes a power optical amplifier 1196 that is capableof amplifying (and which, when supplied with suitable seed signals andoptical pump light, does amplify) high-power optical signals (e.g., suchthat, in various embodiments, the output pulses have a peak power of atleast 10,000 watts, or at least 100,000 watts or even at least 1,000,000watts).

In some embodiments, power amplifier 1196 includes a plurality of pumplasers 1192 that are connected by optical fibers 1193 to a pump combiner1194 that inserts the seed signal into a core of gain fiber 210. In someembodiments, a “backward tap” to obtain a portion of anybackward-propagating light coming from delivery fiber 231 is provided,and this backward-propagating light is coupled to one or more sensors1177. In some embodiments, the sensors 1177 generate one or moreelectrical signals to controller 1195 that are each indicative of thedifferent respective optical properties of the backward-tap signal thatwere measured by sensors 1177.

In some embodiments, sensors 1176 receive a portion of theforward-propagating light coming from gain fiber 210 and generate one ormore electrical signals to controller 1195 that are each indicative ofthe different respective optical properties of the forward-tap signalthat were measured by sensors 1176. In some embodiments, controller 1195is used to control one or more operations of system 1101 (e.g., in someembodiments, controller 1195 can turn off the electrical power to thepump lasers 1192 via electrical control or power line(s) 1197, and/orcan alter the operation of the seed source 209 via electrical control orpower line(s) 1198 (e.g., in some embodiments, if the backward tap andsensors 1177 indicate excess reflected power (or ASE (amplifiedspontaneous emission) or SBS (stimulated Brillouin scattering) or othernoise from downstream optical amplifiers) from delivery fiber 231 intothe gain fiber 210, controller 1195 can force the seed source 209 toemit a continuous-wave (CW) signal that would bleed the excess storedenergy from the gain fiber).

FIG. 11B is a block diagram of an improved optical laser system 1102that includes an optical gain fiber 210 having a core interfaced througha feedback-isolation-and-adaptor unit 1120′ to a multi-mode deliveryfiber 231 having a non-circular core, wherein thefeedback-isolation-and-adaptor unit 1120′ includes mirror 1175B,according to some embodiments of the present invention. In someembodiments, optical laser system 1102 is substantially similar tooptical laser system 1101 shown in FIG. 11A and described above expectthat mirror 1175B of FIG. 11B is configured to reflect a majority offorward-propagating amplified signal 98 and to transmit a minorityportion 98′ of the amplified signal 98 for analysis purposes, accordingto some embodiments of the present invention. In some embodiments,reflecting a majority of the forward-propagating amplified signal 98with mirror 1175B, as opposed to passing a majority of the amplifiedsignal 98 through mirror 1175B, prevents the possible overheating of themirror 1175B and distortion and degradation of the amplified opticalsignal 98 due to mirror 1175B absorbing power from amplified signal 98.

In some embodiments, mirror 1175B reflects about 99.5% of the incidentamplified signal 98 and transmits about 0.5% of the incident amplifiedsignal. In some other embodiments, mirror 1175B reflects about 99.0% ofthe incident amplified signal 98 and transmits about 1.0% of theincident amplified signal. In some other embodiments, mirror 1175Breflects about 98.5% of the incident amplified signal 98 and transmitsabout 1.5% of the incident amplified signal. In some other embodiments,mirror 1175B reflects about 98.0% of the incident amplified signal 98and transmits about 2.0% of the incident amplified signal. In some otherembodiments, mirror 1175B reflects about 95.0% of the incident amplifiedsignal 98 and transmits about 5.0% of the incident amplified signal. Insome other embodiments, mirror 1175B reflects about 90.0% of theincident amplified signal 98 and transmits about 10.0% of the incidentamplified signal.

In some embodiments, the non-circular core of the deliver fiber isdefined by photonic crystal structures such as U.S. Patent Publication2003/0165313 by Broeng et al., which published Sep. 4, 2003 titled“Optical fibre with high numerical aperture, method of its production,and use thereof” which is incorporated herein by reference, (excepthaving a non-circular core defined by the photonic crystal structures)or such as longitudinal holes similar to those as described in U.S. Pat.No. 7,391,561 titled “Fiber- or rod-based optical source featuring alarge-core, rare-earth-doped photonic-crystal device for generation ofhigh-power pulsed radiation and method” that issued Jun. 24, 2008 toFabio Di Teodoro et al., except using larger hole sizes and/or smallerhole spacings (in order to create a large numerical aperture and thuspromote mixing and/or multimode propagation) and having substantially nodoping with species that absorb light of the signal wavelength. A PCF(photonic-crystal fiber) core having relatively small photonic-crystalholes and relatively large hole-to-hole spacings will have a relativelylow numerical aperture and is typically single moded and the concept ofisolation used in some embodiments of the present invention is based ona multimode core. In some embodiments, the photonic crystal structuresdefine a non-circular core having a relatively high numerical aperture.

In some embodiments, the present invention provides a method thatincludes amplifying an optical signal in an optical-gain-fibersubsystem, wherein the optical-gain-fiber subsystem includes an outputend, outputting the amplified optical signal in a forward-propagatingdirection from the output end of the optical-gain-fiber subsystem as ahigh-brightness optical beam having a first Rayleigh range, receivingthe amplified optical signal from the output end of theoptical-gain-fiber subsystem into a first end of a delivery fiber havinga non-circular waveguide core, wherein the delivery fiber is interfacedto the optical-gain-fiber subsystem, outputting the amplified opticalsignal from a second end of the delivery fiber wherein the deliveryfiber includes a non-circular waveguide core, and, without the use of anon-linear optical isolator, inhibiting light traveling in abackward-propagating direction in the delivery fiber from entering theoptical-gain-fiber subsystem in the backward-propagating direction.

In some embodiments of the method, inhibiting of light traveling in abackward-propagating direction further includes offsetting alight-propagation axis of light exiting the output end of theoptical-gain-fiber subsystem from a light-propagation axis of lightexiting the first end of the delivery fiber relative to one another suchthat a majority of the light traveling in the backward-propagatingdirection and emitted from the first end of the delivery fiber does notenter a core of the optical-gain-fiber subsystem.

In some embodiments of the method, the light traveling in thebackward-propagating direction in the delivery fiber that exits thefirst end of the delivery fiber toward the optical-gain-fiber subsystemhas a second Rayleigh range that is shorter than the first Rayleighrange of the optical signal output from the optical-gain-fibersubsystem.

Some embodiments of the method further include providing an aperturelocated between the output end of the optical-gain-fiber subsystem andthe first end of the delivery fiber, passing a majority of theforward-propagating optical signal through the aperture, blocking amajority portion of the light traveling in the backward-propagatingdirection that exits the first end of the delivery fiber toward theoptical-fiber amplifier subsystem, and preventing a majority portion ofthe light traveling in the backward-propagating direction from enteringthe output end of the optical-gain-fiber subsystem.

Some embodiments of the method further include providing an endcapattached to the first end of the delivery fiber, providing an aperturein the endcap and located between the output end of theoptical-gain-fiber subsystem and the first end of the delivery fiber,passing a majority of the forward-propagating optical signal through theaperture, blocking a majority portion of the light traveling in thebackward-propagating direction that exits the first end of the deliveryfiber toward the optical-fiber amplifier subsystem; and, preventing amajority portion of the light traveling in the backward-propagatingdirection from entering the output end of the optical-gain-fibersubsystem.

Some embodiments of the method further include providing a first lensand a second lens separated by a first distance, optically coupling thefirst lens to the output end of the optical-gain-fiber subsystem and tothe second lens, optically coupling the second lens to the first lensand to the first end of the delivery fiber, collimating theforward-propagating optical signal from the optical-gain-fiber subsystemusing the first lens, and receiving the collimated forward-propagatingoptical signal from the first lens and focusing the forward-propagatingoptical signal using the second lens such that the forward-propagatingoptical signal enters the first end of the delivery fiber.

In some embodiments of the method, the first distance is greater thanthe second Rayleigh range, and the first distance is not greater thanthe first Rayleigh range. In other embodiments of the method, the firstdistance is greater than the second Rayleigh range, and the firstdistance is less than the first Rayleigh range.

Some embodiments of the method further include providing a reflectingoptical element located between the first lens and the second lens,reflecting the forward-propagating optical signal and the lighttraveling in the backward-propagating direction using the reflectingoptical element in order to increase a distance the forward-propagatingoptical signal and the light traveling in the backward-propagatingdirection travel between the first lens and the second lens.

Some embodiments of the method further include folding an optical pathof the forward-propagating light between the first lens and the secondlens.

Some embodiments of the method further include providing a reflectingoptical element located between the optical-gain-fiber subsystem and thedelivery fiber, reflecting the forward-propagating optical signal andthe light traveling in the backward-propagating direction using thereflecting optical element in order to increase a distance theforward-propagating optical signal and the light traveling in thebackward-propagating direction travel between the optical-gain-fibersubsystem and the delivery fiber.

Some embodiments of the method further include providing a reflectingoptical element located between the optical-gain-fiber subsystem and thedelivery fiber, reflecting the forward-propagating optical signal andthe light traveling in the backward-propagating direction using thereflecting optical element in order to shorten a footprint of theoptical-gain-fiber subsystem while providing a suitable distance theforward-propagating optical signal and the light traveling in thebackward-propagating direction travel between the optical-gain-fibersubsystem and the delivery fiber. In some embodiments, the suitabledistance is a distance that is longer than a spacing between theoptical-gain-fiber subsystem and the delivery fiber.

Some embodiments of the method further include folding an optical pathbetween the optical-gain-fiber subsystem and the delivery fiber.

In some embodiments of the method, the delivery fiber has a sufficientlylarge numerical aperture such that substantially all of the light outputfrom the optical-gain-fiber subsystem enters the non-circular core ofthe delivery fiber.

In some embodiments of the method, the numerical aperture of thedelivery fiber is between about 0.2 and about 0.6.

In some embodiments, the present invention provides an apparatus thatincludes an optical-fiber amplifier subsystem configured to amplify anoptical signal, wherein the optical-fiber amplifier subsystem includesan output end, and wherein the output end of the optical-fiber amplifiersubsystem is configured to output the optical signal in aforward-propagating direction as a high-brightness optical beam having afirst Rayleigh range, and a delivery fiber that has an interface to theoptical-fiber amplifier subsystem and that has a first end and a secondend, wherein the delivery fiber is configured to receive the opticalsignal from the output end of the optical-fiber amplifier subsystem intothe first end of the delivery fiber, and wherein the delivery fiber isconfigured to output the optical signal from the second end of thedelivery fiber, wherein the delivery fiber includes a non-circularwaveguide core, and wherein the apparatus is configured such that lighttraveling in a backward-propagating direction in the delivery fiber issubstantially prevented from entering the optical-fiber amplifiersubsystem in the backward-propagating direction.

In some embodiments, the apparatus is configured such that an axis ofthe output end of the optical-fiber amplifier subsystem and an axis ofthe first end of the delivery fiber are offset relative to one anothersuch that a majority of the light traveling in the backward-propagatingdirection and emitted from the first end of the delivery fiber does notenter a core of the optical-fiber amplifier subsystem.

In some embodiments, the light traveling in the backward-propagatingdirection in the delivery fiber that exits the first end of the deliveryfiber toward the optical-fiber amplifier subsystem has a second Rayleighrange that is shorter than the first Rayleigh range of theforward-propagating optical signal output from the optical optical-fiberamplifier subsystem.

In some embodiments, the apparatus is configured such that an opticalaxis of the output end of the optical amplifier and an axis of the firstend of the delivery fiber are aligned offset relative to one anothersuch that a majority of light reflected from the second end of thedelivery fiber and emitted from the first end of the delivery fiber doesnot enter a core of the optical-amplifier subsystem.

In some embodiments, the apparatus further includes an aperture locatedbetween the output end of the optical-fiber amplifier subsystem and thefirst end of the delivery fiber, wherein the aperture is configured topass a majority of the forward-propagating optical signal through theaperture and wherein the aperture is configured to block a majorityportion of the light traveling in the backward-propagating directionthat exits the first end of the delivery fiber toward the optical-fiberamplifier subsystem from entering the output end of the optical-fiberamplifier subsystem.

In some embodiments, the apparatus further includes a first lensoptically coupled to the output end of the optical-fiber amplifiersubsystem, wherein the first lens is configured to substantiallycollimate the forward-propagating optical signal from the optical-fiberamplifier subsystem, a second lens optically coupled to the first end ofthe delivery fiber, wherein the second lens is configured to receive thecollimated forward-propagating optical signal from the first lens and tofocus the forward-propagating optical signal such that theforward-propagating optical signal enters the first end of the deliveryfiber, and wherein the first lens and the second lens are separated by afirst distance.

In some embodiments, the first distance is greater than the secondRayleigh range, and the first distance is not greater than the firstRayleigh range.

In some embodiments, the first distance is greater than the secondRayleigh range, and the first distance is less than the first Rayleighrange.

In some embodiments, the apparatus further includes a reflecting opticalelement located between the optical-fiber amplifier subsystem and thedelivery fiber, wherein the reflecting optical element is configured toprovide at least one reflection of the forward-propagating opticalsignal and of the light traveling in the backward-propagating directionin order to fold an optical path of the forward-propagating opticalsignal and of the light traveling in the backward-propagating directionbetween the optical-fiber amplifier subsystem and the delivery fiber.

In some embodiments, the apparatus further includes a reflecting opticalelement located between the first lens and the second lens, wherein thereflecting optical element is configured to provide at least onereflection of the forward-propagating optical signal and of the lighttraveling in the backward-propagating direction in order to fold anoptical path of the forward-propagating optical signal and of the lighttraveling in the backward-propagating direction between the first lensand the second lens.

In some embodiments, the delivery fiber is configured to have asufficiently large numerical aperture (e.g., in some embodiments, an NAthat is no less than 0.1) such that substantially all of the lightoutput from the signal fiber enters the non-circular core of thedelivery fiber.

In some embodiments, the apparatus further includes a partiallyreflecting mirror located between the first lens and the second lens,wherein the partially reflecting mirror is configured to reflect aminority portion of the collimated forward-propagating optical signalfrom the first lens to a first sensor and to transmit a majority portionof the collimated forward-propagating optical signal to the second lens,and wherein the reflecting mirror is further configured to reflect aminority portion of the light traveling in the backward-propagatingdirection to a second sensor.

In some embodiments, the apparatus further includes a partiallyreflecting mirror located between the first lens and the second lens,wherein the partially reflecting mirror is configured to reflect amajority portion of the collimated forward-propagating optical signalfrom the first lens to the second lens, and wherein the reflectingmirror is further configured to transmit a minority portion of theforward-propagating light toward a first sensor and to transmit aminority portion of the backward-propagating optical signal to a secondsensor.

In some embodiments, the present invention provides a method thatincludes providing a delivery fiber assembly having a reverse endcap anda fiber portion, optically coupling the reverse endcap and the fiberportion, wherein the reverse endcap has a solid first core having afirst core diameter, wherein the fiber portion has a non-circular secondcore having a second core diameter; and wherein the first core diameteris larger than the second core diameter.

Some embodiments of the method further include receiving aforward-propagating optical signal into the solid first core of thereverse endcap, passing a majority of the forward-propagating opticalsignal into the non-circular second core with substantially nodegradation in brightness, wherein light traveling in abackward-propagating direction has a brightness that is degraded by thereverse endcap.

Some embodiments of the method further include providing anoptical-amplifier subsystem, wherein the optical-amplifier subsystem hasan output adaptor attaching a connector to the first endcap of thedelivery fiber, wherein the adaptor and the connector are configured toreleasably connect and disconnect with each other.

Some embodiments of the method further include providing a removablesterile enclosure, inserting the delivery fiber into the removablesterile enclosure, sealing the removable sterile enclosure andsterilizing both such that the delivery fiber is kept in a sterilecondition until use, and wherein the delivery fiber is replaceablyconnectable to the optical-amplifier subsystem, and wherein the deliveryfiber is optionally disposable.

In some embodiments of the method, the first endcap has a multi-modecore and the fiber portion has a multi-mode core.

In some embodiments of the method, the non-circular second core has asubstantially polygonal-shaped.

In some embodiments of the method, the first endcap and the fiberportion delivery fiber each have a sufficiently large numerical aperturesuch that substantially all of the forward-propagating optical signalenters the non-circular core of the fiber portion.

In some embodiments of the method, the numerical aperture of thedelivery fiber is between about 0.2 and about 0.3. In some embodimentsof the method, the numerical aperture of the delivery fiber is betweenabout 0.3 and about 0.4. In some embodiments of the method, thenumerical aperture of the delivery fiber is between about 0.4 and about0.5. In some embodiments of the method, the numerical aperture of thedelivery fiber is between about 0.5 and about 0.6.

In some embodiments of the method, the non-circular second core has asubstantially square shape.

In some embodiments of the method, the non-circular second core includesa substantially oval shape.

In some embodiments, the present invention provides an apparatus thatincludes a delivery fiber having a reverse endcap and a fiber portionoptically coupled to the reverse endcap, wherein the reverse endcap hasa solid first core having a first core diameter, wherein the fiberportion has a non-circular second core having a second core diameter,and wherein the first core diameter is larger than the second corediameter.

In some embodiments of the apparatus, the delivery fiber is configuredto receive a forward-propagating optical signal into the solid firstcore of the reverse endcap and pass a majority of theforward-propagating optical signal into the non-circular second corewith substantially no degradation in brightness, while the reverseendcap does degrade brightness of light traveling in abackward-propagating direction opposite the forward-propagating opticalsignal.

In some embodiments of the apparatus, the apparatus further includes anoptical-amplifier subsystem having an output adaptor mechanicallyconnected to the optical-amplifier subsystem, wherein the delivery fiberhas a connector mechanically connected to the delivery fiber, andwherein the adaptor and the connector are configured to releasablyconnect to and disconnect from each other.

In some embodiments of the apparatus, the first endcap has a multi-modecore and the fiber portion has a multi-mode core.

In some embodiments of the apparatus, the apparatus further includes aremovable sterile enclosure surrounding the delivery fiber for holdingthe delivery fiber in a sterile condition until use, wherein thedelivery fiber is replaceably connectable to the optical-amplifiersubsystem, and wherein the delivery fiber is disposable.

In some embodiments of the apparatus, the non-circular second core has asubstantially polygonal-shaped.

In some embodiments of the apparatus, the first endcap and the fiberportion delivery fiber each have a sufficiently large numerical aperturesuch that substantially all of the forward-propagating optical signalenters the non-circular core of the fiber portion. In some embodiments,the numerical aperture of the delivery fiber is between about 0.2 andabout 0.3. In some embodiments, the numerical aperture of the deliveryfiber is between about 0.3 and about 0.4. In some embodiments, thenumerical aperture of the delivery fiber is between about 0.4 and about0.5. In some embodiments, the numerical aperture of the delivery fiberis between about 0.5 and about 0.6. In some embodiments, the numericalaperture of the delivery fiber is between about 0.6 and about 0.75.

In some embodiments of the apparatus, the non-circular second core has asubstantially square shape.

In some embodiments of the apparatus, the non-circular second core has asubstantially oval shape.

In some embodiments of the apparatus, the non-circular second core has asubstantially polygonal-shaped.

In some embodiments of the apparatus, the non-circular second core isdefined by and surrounded by an airclad region.

In some embodiments of the apparatus, the non-circular second coreincludes stress rods.

In some embodiments, the present invention provides an apparatus thatincludes for delivering a forward-propagating signal to a destinationfrom a signal-providing fiber having an output end, the apparatuscomprising, a delivery fiber having a first end and a second end,wherein forward-propagating light travels to the second end from thefirst end and backward-propagating light travels to the first end fromthe second end, and wherein the delivery fiber includes a non-circularwaveguide core and a cladding layer surrounding the non-circularwaveguide core, and a first endcap that is connected to the first end ofthe delivery fiber, wherein the endcap operates to pass a majority offorward-propagating signal light output from the signal-providing fiberinto the delivery fiber and pass less than a majority ofbackward-propagating light into the output end of the signal-providingfiber from the second end of the delivery fiber. In some embodiments,the endcap operates to pass at least 60% of the forward-propagatingsignal light output and pass no more than 40% of backward-propagatinglight. In some embodiments, the endcap operates to pass at least 70% ofthe forward-propagating signal light output and pass no more than 30% ofbackward-propagating light. In some embodiments, the endcap operates topass at least 80% of the forward-propagating signal light output andpass no more than 20% of backward-propagating light. In someembodiments, the endcap operates to pass at least 90% of theforward-propagating signal light output and pass no more than 10% ofbackward-propagating light. In some embodiments, the endcap operates topass at least 95% of the forward-propagating signal light output andpass no more than 5% of backward-propagating light. In some embodiments,the endcap operates to pass at least 98% of the forward-propagatingsignal light output and pass no more than 2% of backward-propagatinglight.

In some embodiments, the endcap includes an aperture, wherein theaperture passes the majority of forward-propagating signal light that isoutput from the signal-providing fiber into the delivery fiber andwherein the aperture blocks a majority of the backward-propagatingsignal light. In some embodiments, the aperture operates to pass atleast 60% of the forward-propagating signal light output and pass nomore than 40% of backward-propagating light. In some embodiments, theaperture operates to pass at least 70% of the forward-propagating signallight output and pass no more than 30% of backward-propagating light. Insome embodiments, the aperture operates to pass at least 80% of theforward-propagating signal light output and pass no more than 20% ofbackward-propagating light. In some embodiments, the aperture operatesto pass at least 90% of the forward-propagating signal light output andpass no more than 10% of backward-propagating light. In someembodiments, the aperture operates to pass at least 95% of theforward-propagating signal light output and pass no more than 5% ofbackward-propagating light. In some embodiments, the aperture operatesto pass at least 98% of the forward-propagating signal light output andpass no more than 2% of backward-propagating light.

In some embodiments of the apparatus, the non-circular waveguide core isdefined by and surrounded by an air-clad region.

In some embodiments of the apparatus, the non-circular waveguide coreincludes stress-rods.

In some embodiments of the apparatus, the non-circular waveguide corehas a shape that is substantially polygonal.

In some embodiments of the apparatus, the non-circular waveguide corehas a shape that is substantially square.

In some embodiments of the apparatus, the non-circular waveguide corehas a shape that is substantially oval.

In some embodiments, an optical axis of the first end of the deliveryfiber is tilted relative to an optical axis of the output end of thesignal-providing fiber in order to reduce back reflected light from thedelivery fiber from entering the signal-providing fiber.

In various embodiments, the tilt angle is substantially 1°, orsubstantially 2°, or substantially 3°, or substantially 4°, orsubstantially 5°, or substantially 6°, or substantially 7°, orsubstantially 8°, or substantially 9°, or substantially 10°. In someembodiments, the tilt angle is at least 5°, or at least 10°, or at least15°, or at least 20°.

In some embodiments, a central optical axis of the first end of thedelivery fiber is substantially parallel but laterally offset relativeto a central optical axis of the output end of the signal-providingfiber in order to reduce back reflected light from the delivery fiberfrom entering the signal-providing fiber.

In various embodiments, the lateral offset amount between the centraloptical axis of the first end of the delivery fiber and the centraloptical axis of the output end of the signal-providing fiber is at least5 microns, or at least 10 microns, or at least 15 microns, or at least20 microns, or at least 25 microns, or at least 30 microns, or at least35 microns, or at least 40 microns, or at least 45 microns, or at least50 microns, or at least 75 microns, or at least 100 microns, or at least250 microns.

In some of the embodiments, the delivery fiber is configured to have asufficiently large numerical aperture such that substantially all of thelight output from the signal fiber enters the non-circular core of thedelivery fiber.

In various ones of the embodiments, the numerical aperture of thedelivery fiber is between about 0.1 and about 0.6, between about 0.1 andabout 0.12, between about 0.12 and about 0.15, between about 0.1 andabout 0.15, between about 0.15 and about 0.2, between about 0.2 andabout 0.3, between about 0.3 and about 0.4, between about 0.4 and about0.5, between about 0.5 and about 0.6, or between about 0.6 and about0.7. In general, by using non-circular fibers the NA fills very fast,i.e. in a short distance. For circular fibers the fundamental mode canpropagate a long distance and then one should specify the NA of thefundamental mode.

In various ones of the embodiments, the numerical aperture of the outputend of the signal source is about 0.01, about 0.02, about 0.05, about0.1, about 0.12, about 0.15, about 0.18, about 0.2, about 0.25, about0.3, or larger than about 0.3.

In some of the embodiments, the delivery fiber is configured topropagate a plurality of modes of light through the delivery fiber(i.e., in some embodiments, the delivery fiber is a multimode fiber).

In some of the embodiments, the entry aperture of the delivery fiber isnon-circular.

In some of the embodiments, the entry aperture of the delivery fiber islaterally offset from an optical axis of the endcap.

In some of the embodiments, the entry aperture is non-centered withrespect to the longitudinal axis of the non-circular core of thedelivery fiber.

In some of the embodiments, the delivery fiber is connectorized anddisposable.

In some of the embodiments, the delivery fiber is sterilized andenclosed in a sealed removable package.

Some embodiments of the apparatus further include an optical-amplifiersubsystem having a first output connector mechanically connected to theoptical-amplifier subsystem, wherein the delivery fiber has a secondconnector mechanically connected to delivery fiber, and wherein thefirst connector and the second connector are configured to releasablyconnect and disconnect with each other.

Some embodiments of the apparatus further include a medical instrumentthat includes an electrical power supply, a controller operably coupledto receive power from the electrical power supply, an optical-signalsource operably coupled to be controlled by the controller and having afirst output connector mechanically connected to the optical-signalsource, wherein the delivery fiber has a second connector mechanicallyconnected to delivery fiber, and wherein the first connector and thesecond connector are configured to releasably connect and disconnectwith each other.

In some embodiments, the present invention provides a system thatincludes an optical-fiber amplifier subsystem that amplifies an opticalsignal, wherein the optical-fiber amplifier subsystem includes an outputend, and wherein the output end is outputs the optical signal; and adelivery fiber having a first end and a second end, wherein the deliveryfiber receives the optical signal from the output end of theoptical-fiber amplifier subsystem into the first end of the deliveryfiber and outputs the optical signal from the second end of the deliveryfiber, wherein the delivery fiber includes a non-circular waveguidecore.

In some embodiments of the system, light traveling in thebackward-propagating direction from the second end of the delivery fibertoward the first end of the delivery fiber exits the first end of thedelivery fiber toward the output end of the optical-amplifier subsystemhaving a reflected-light-signal Rayleigh range that is shorter than thefirst Rayleigh range of the optical beam of the optical-amplifiersubsystem.

In some embodiments, the system is configured such that a longitudinalaxis of the output end of the optical-amplifier subsystem and alongitudinal axis of the first end of the delivery fiber are alignedoffset relative to one another such that a majority of light travelingin the backward-propagating direction and emitted from the first end ofthe delivery fiber does not enter a core of the optical-amplifiersubsystem.

In some embodiments, the system is configured such that an axis of theoutput end of the optical-amplifier subsystem and an axis of the firstend of the delivery fiber are aligned offset relative to one anothersuch that a majority of light reflected from the second end of thedelivery fiber and emitted from the first end of the delivery fiber doesnot enter a core of the optical-amplifier subsystem.

In some embodiments, the present invention provides a method fordelivering a forward-propagating signal to a destination from asignal-providing fiber having an output end through a delivery fiber,the method including providing the delivery fiber, the delivery fiberhaving a first end and a second end, wherein forward-propagating lightin the delivery fiber travels to the second end from the first end andbackward-propagating light travels to the first end from the second end,wherein the delivery fiber includes a non-circular waveguide core, acladding layer surrounding the non-circular waveguide core, and a firstendcap that is connected to the first end of the delivery fiber, andwherein the delivery fiber and the endcap are free of any non-linearoptical isolator. This method further includes passing a majority offorward-propagating signal light output from the signal-providing fiberinto the delivery fiber; and passing less than a majority of light ofback-reflected light into the output end of the signal-providing fiberfrom the second end of the delivery fiber.

In some embodiments of the method, the forward-propagating signal lightis not optically isolated with non-linear optics. In some embodiments ofthe method, the providing of the delivery fiber includes forming thenon-circular waveguide core having a shape that is substantiallypolygonal. In some embodiments of the method, the providing of thedelivery fiber includes forming the non-circular waveguide core having ashape that is substantially square. In some embodiments of the method,the providing of the delivery fiber includes forming the non-circularwaveguide core having a shape that is substantially oval.

In some embodiments of the method, the providing of the delivery fiberincludes tilting an optical axis of the first end of the delivery fiberrelative to an optical axis of the output end of the signal-providingfiber in order to reduce back reflected light from the delivery fiberfrom entering the signal-providing fiber. In some other embodiments ofthe method, the providing of the delivery fiber includes positioning acentral optical axis of the first end of the delivery fiber to besubstantially parallel but laterally offset relative to a centraloptical axis of the output end of the signal-providing fiber in order toreduce back reflected light from the delivery fiber from entering thesignal-providing fiber.

In some embodiments of the method, the providing of the delivery fiberincludes providing the delivery fiber with a sufficiently largenumerical aperture such that substantially all of the light output fromthe signal fiber enters the non-circular core of the delivery fiber. Insome embodiments of the method, the numerical aperture of the deliveryfiber is between about 0.2 and about 0.3. In some embodiments of themethod, the numerical aperture of the output end of the signal source isbetween about 0.01 and about 0.15.

In some embodiments of the method, the passing of the majority offorward-propagating signal light output includes propagating multiplemodes of light through the delivery fiber. In some embodiments of themethod, the providing of the delivery fiber includes making the entryaperture of the delivery fiber non-circular.

In some embodiments, the method further includes laterally offsettingthe entry aperture of the delivery fiber from a central optical axis ofthe endcap. In some embodiments, the method further includesnon-centering the entry aperture with respect to the non-circular coreof the delivery fiber. In some embodiments, the method further includesconnectorizing the delivery fiber, wherein the delivery fiber issingle-use and disposable. In some embodiments, the method furtherincludes sterilizing the delivery fiber and enclosing the delivery fiberin a sealed removable package. In some such embodiments, the sterilizingof the delivery fiber is done after the enclosing of the delivery fiberin a sealed removable package. In some embodiments, the delivery fiberis then stored until needed, then removed from the package, attached tothe gain fiber, and used.

In some embodiments, the method further includes providing anoptical-amplifier subsystem having a first output connector mechanicallyconnected to the optical-amplifier subsystem; mechanically connecting asecond connector to the delivery fiber; and releasably connecting thefirst connector and the second connector with each other.

In some embodiments, the method further includes providing a medicalinstrument that includes: an electrical power supply, a controlleroperably coupled to receive power from the electrical power supply, anoptical-signal source operably coupled to be controlled by thecontroller and having a first output connector mechanically connected tothe optical-signal source, mechanically connecting a second connector tothe delivery fiber; and releasably connecting the first connector andthe second connector with each other.

In some embodiments, the present invention provides an apparatus thatincludes means for amplifying an optical signal, the means (as describedherein and equivalents thereof) for amplifying having an output end;means (as described herein and equivalents thereof) for outputting theamplified optical signal in a forward-propagating direction from theoutput end as a high-brightness optical beam having a first Rayleighrange; non-circular waveguide means for delivering an optical signal;means (as described herein and equivalents thereof) for receiving theamplified optical signal from the output end of the means for amplifyinginto a first end of the non-circular waveguide means for delivering;means (as described herein and equivalents thereof) for interfacing thenon-circular waveguide means for delivering to the means for amplifying;means (as described herein and equivalents thereof) for outputting theamplified optical signal from a second end of the non-circular waveguidemeans for delivering; and means (as described herein and equivalentsthereof) for inhibiting light traveling in a backward-propagatingdirection in the non-circular waveguide means for delivering fromentering the means for amplifying in the backward-propagating direction.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Although numerous characteristics andadvantages of various embodiments as described herein have been setforth in the foregoing description, together with details of thestructure and function of various embodiments, many other embodimentsand changes to details will be apparent to those of skill in the artupon reviewing the above description. The scope of the invention should,therefore, be determined with reference to the appended claims, alongwith the full scope of equivalents to which such claims are entitled. Inthe appended claims, the terms “including” and “in which” are used asthe plain-English equivalents of the respective terms “comprising” and“wherein,” respectively. Moreover, the terms “first,” “second,” and“third,” etc., are used merely as labels, and are not intended to imposenumerical requirements on their objects.

What is claimed is:
 1. A method comprising: amplifying an optical signalin an optical-gain-fiber subsystem of a laser system, wherein theoptical-gain-fiber subsystem includes an output end; outputting theamplified optical signal in a forward-propagating direction from theoutput end of the optical-gain-fiber subsystem; receiving the amplifiedoptical signal from the output end of the optical-gain-fiber subsysteminto a first end of a delivery fiber; outputting the amplified opticalsignal from a second end of the delivery fiber; and without the use of anon-linear optical isolator, inhibiting light traveling in abackward-propagating direction in the delivery fiber from entering theoptical-gain-fiber subsystem in the backward-propagating direction,wherein the inhibiting includes tilting an optical axis of the first endof the delivery fiber relative to a light-propagation axis of theamplified optical signal exiting the optical-gain-fiber subsystem suchthat a non-zero angle is formed between the tilted optical axis of thefirst end and the light-propagation axis of the amplified opticalsignal.
 2. The method of claim 1, further comprising: providing areverse endcap on the first end of the delivery fiber, wherein thereverse endcap further degrades the light traveling in thebackward-propagating direction and thus further reduces thebackward-traveling light that enters the optical-gain-fiber subsystem.3. The method of claim 1, further comprising: providing a first lens anda second lens; optically coupling the first lens to the output end ofthe optical-gain-fiber subsystem, optically coupling the second lens tothe first end of the delivery fiber, and optically coupling the firstlens to the second lens, wherein the optically coupling of the firstlens to the second lens includes separating the first lens from thesecond lens by a first distance such that the light traveling in thebackward-propagating direction diverges and overfills the first lens;collimating the forward-propagating optical signal from theoptical-gain-fiber subsystem using the first lens; and receiving thecollimated forward-propagating optical signal from the first lens andfocusing the forward-propagating optical signal using the second lenssuch that the forward-propagating optical signal enters the first end ofthe delivery fiber.
 4. The method of claim 1, further comprising:providing a first lens and a second lens; optically coupling the firstlens to the output end of the optical-gain-fiber subsystem, opticallycoupling the second lens to the first end of the delivery fiber, andoptically coupling the first lens to the second lens; reflecting theforward-propagating optical signal a plurality of times and reflectingthe light traveling in the backward-propagating direction a plurality oftimes in order to increase a distance the forward-propagating opticalsignal and the light traveling in the backward-propagating directiontravel between the first lens and the second lens.
 5. The method ofclaim 1, further comprising: mode mixing the forward-propagating lightin the delivery fiber by a geometry of the delivery fiber.
 6. The methodof claim 1, wherein the inhibiting of light traveling in thebackward-propagating direction further includes offsetting thelight-propagation axis of the amplified optical signal relative to theoptical axis of the first end of the delivery fiber such that a majorityof the light traveling in the backward-propagating direction from thedelivery fiber does not enter a core of the optical-gain-fibersubsystem.
 7. The method of claim 1, surrounding a waveguide core of thedelivery fiber with a photonic-crystal layer and surrounding thephotonic-crystal layer with a cladding layer.
 8. The method of claim 1,further comprising connectorizing the delivery fiber.
 9. The method ofclaim 1, further comprising: tapping the forward-propagating light toobtain a forward-tap signal; tapping the backward-propagating light toobtain a backward-tap signal; and controlling operation of the lasersystem based on the forward-tap signal and the backward-tap signal. 10.An apparatus comprising: an optical-fiber amplifier subsystem configuredto amplify an optical signal, wherein the optical-fiber amplifiersubsystem includes an output end, and wherein the output end of theoptical-fiber amplifier subsystem is configured to output the amplifiedoptical signal in a forward-propagating direction; and a delivery fiberthat has an interface to the optical-fiber amplifier subsystem and thathas a first end and a second end, wherein the delivery fiber isconfigured to receive the optical signal from the output end of theoptical-fiber amplifier subsystem into the first end of the deliveryfiber, wherein the delivery fiber is configured to output the opticalsignal from the second end of the delivery fiber, and wherein an opticalaxis of the first end of the delivery fiber is tilted relative to alight-propagation axis of the amplified optical signal exiting theoptical-fiber amplifier subsystem such that a non-zero angle is formedbetween the titled optical axis of the first end and thelight-propagation axis of the amplified optical signal and such thatlight traveling in a backward-propagating direction in the deliveryfiber is inhibited from entering the optical-fiber amplifier subsystem.11. The apparatus of claim 10, further comprising a reverse endcaplocated between the output end of the optical-fiber amplifier subsystemand the first end of the delivery fiber, wherein the reverse endcap isconfigured to further degrade the light traveling in thebackward-propagating direction and thus further reduce thebackward-traveling light that enters the optical-fiber amplifiersubsystem.
 12. The apparatus of claim 10, further comprising: a firstlens optically coupled to the output end of the optical-fiber amplifiersubsystem, wherein the first lens is configured to substantiallycollimate the forward-propagating optical signal from the optical-fiberamplifier subsystem; and a second lens optically coupled to the firstend of the delivery fiber, wherein the second lens is configured toreceive the collimated forward-propagating optical signal from the firstlens and to focus the forward-propagating optical signal such that theforward-propagating optical signal enters the first end of the deliveryfiber.
 13. The apparatus of claim 10, further comprising: a first lensoptically coupled to the output end of the optical-fiber amplifiersubsystem; a second lens optically coupled to the first end of thedelivery fiber and optically coupled to the first lens; and at least onereflecting optical element located between the first lens and the secondlens, wherein the at least one reflecting optical element is configuredto reflect the forward-propagating optical signal a plurality of timesand to reflect the light traveling in the backward-propagating directiona plurality of times in order to increase a distance theforward-propagating optical signal and the light traveling in thebackward-propagating direction travel between the first lens and thesecond lens.
 14. The apparatus of claim 10, wherein the delivery fiberincludes a non-circular waveguide core.
 15. The apparatus of claim 10,wherein the light-propagation axis of the amplified optical signal andthe optical axis of the first end of the delivery fiber are offsetrelative to one another such that a majority of the light traveling inthe backward-propagating direction from the delivery fiber does notenter a core of the optical-fiber amplifier subsystem.
 16. The apparatusof claim 10, wherein a waveguide core of the delivery fiber issurrounded by a photonic-crystal layer, and wherein the photonic-crystallayer is surrounded by a cladding layer.
 17. The apparatus of claim 10,wherein the delivery fiber includes a non-circular waveguide coresurrounded by a photonic-crystal layer, and wherein the non-circularwaveguide core includes a mask having an offset light-entry aperturesuch that a majority of the light traveling in the backward-propagatingdirection from the first end of the delivery fiber is blocked by themask and does not enter a core of the optical-fiber amplifier subsystem.18. The apparatus of claim 10, further comprising a connector thatincludes a cylindrical hole that extends from a first end of theconnector to a second end of the connector, wherein the connector isconfigured to receive the delivery fiber.
 19. The apparatus of claim 10,further comprising a feedback-isolation-and-adaptor unit, wherein thefeedback-isolation-and-adapter unit is connected between theoptical-gain-fiber subsystem and the delivery fiber such that the outputend of the optical-gain-fiber subsystem is optically coupled to an inputferrule of the feedback-isolation-and-adapter unit and such that anoutput ferrule of the feedback-isolation-and-adapter unit is opticallycoupled to the first end of the delivery fiber, wherein thefeedback-isolation-and-adapter unit includes a forward-propagating-lighttap and a backward-propagating-light tap.
 20. An apparatus comprising:means for amplifying an optical signal, the means for amplifying havingan output end; means for outputting the amplified optical signal in aforward-propagating direction from the output end; a delivery fiberconfigured to deliver the amplified optical signal; means for receivingthe amplified optical signal from the output end of the means foramplifying into a first end of the delivery fiber; means for interfacingthe delivery fiber to the means for amplifying; means for outputting theamplified optical signal from a second end of the delivery fiber; andmeans for forming a non-zero angle between an optical axis of the firstend of the delivery fiber and a light-propagation axis of the amplifiedoptical signal exiting the means for amplifying such that lighttraveling in a backward-propagating direction in the delivery fiber isinhibited from entering the means for amplifying.